Dissociative identity disorder was previously known as Multiple Personality Disorder (MPD), sometimes incorrectly called "split personality", it is characterized by the presence of more than one sense of identity within a single human body. These alternate identities are commonly known as alters or dissociated parts. A person with multiple identities is often referred to as a multiple.
What are Alters?
Other terms for alter include: alternate identity, dissociative identity, distinct identity, personality state, personality, dissociated part, self-state, part, part of the mind, part of the self, dissociative part of the personality.[1,2] :121
A person with Dissociative Identity Disorder (DID), or a similar form of Other Specified Dissociative Disorder (previously called Dissociative Disorder Not Otherwise Specified, or DDNOS-1) has a fragmented personality. A person with DID experiences himself or herself as having separate identities, known as alters, or alternate identities.:292,  Alters take over control of the person's body or behavior at various times.  Each can function independently. All the alters together make up the person's whole personality. Alters typically develop from dissociation caused by prolonged early childhood trauma, although attachment problems and persistent neglect in very early childhood are also known factors.:189-191 People with alters may refer to their alters as "parts inside, aspects, facets, ways of being, voices, multiples, selves, ages of me, people, persons, individuals, spirits, demons, others," etc. :121 Alter identities are sometimes incorrectly referred to as ego states, or even alter egos, but these states exist in people without alters and do not involve amnesia, dissociative symptoms, or clinical distress.[1, 2] :129
Characteristics of AltersAlters may have
- different ages, for instance much younger or older;
- a different gender to the physical body;
- different names, or no name;
- different roles or functions, either related to daily life or to trauma;
- different attitudes, and preferences, e.g, in food, or dress
- a different perception of their appearance, for e.g., different hair or skin color, body shape;
- different memories, e.g., some may remember trauma or events in daily life that others have amnesia for;
- psychobiological difference to others, e.g., different vision, medication responses, allergies, plasma glucose levels in diabetic patients, heart rate, blood pressure readings, galvanic skin response, muscle tension, laterality, immune function, EEG readings, etc. :293, :120-121, :18, :52, 24:
Different alters have shown different results in neuroimaging tests, including functional magnetic resonance imaging activation, and brain activation and regional blood flow and differences in PET scans. The variability between alters is measurably greater than variability between non-dissociative people who are attempting to simulate alters. :121
Because many alters have a very different perception of their body, they may disown it, or believe strongly that it is a different chronological age, and refer to as "the body" rather than "my body".:120,140 Alters who believe that they have their own, separate physical body, can result in refusing to seek medical care, and self-harm or suicide attempts, in the belief that they will be unaffected since it is not "their" body which is harmed. This can even involve attempting to kill off "others". :132, 140
Negotiating with AltersThis video describes how to negotiate with alters, focusing on alters who are determined to harm or kill the host (the person with DID). These internally homicidal alters may be unaware of the fact that they will also die if the host's body dies.
Types of Alters
All alters can be broadly classed as either Apparently Normal Parts of the Personality (ANPs), or Emotional Parts of the Personality (EPs).:31 In additional, each can have one or more type or role, for example a child alter may also be a protector. People who are "very fragmented" (have a very large number of parts) may also have complex mixtures of ANP and EP.:78
Apparently Normal Parts (ANPs)
This term had previously been called a "host personality" or "host". This is the identity who manages every day life and does not normally hold trauma memories.  There may be more than one ANP managing daily life at any one time, each with different roles. :30 An ANP may be emotionally unconnected to, or amnesiac for, past traumatic events.:101
Emotional Parts (EPs)
Emotional Parts of the Personality (EP) "hold traumatic memory, often being stuck in the sensory experience of the memory and unaware of the passage of time.:21 Tasks involving daily life are managed by ANPs instead, e.g., working, cooking and parenting.:19 All identities within a person can be categorized as ANPs or EPs. Despite their name, some EPs are not emotional.:30
List of Types of AlterAnimal Alters
Abused children may develop animal parts/alters because they identify with animals and consider them friends. Animal parts may be able to express emotions that the Apparently Normal Parts can"t. Animals like tigers may function as protectors, growling when an Apparently Normal Part is distressed. :65 Alters may also become to believe they are animals because abusers either told them they were or treated them like animals, e.g., dog alters. Some abusers are known to force children to act like animals, for example making them bark or use a dog bowl for food. Animal alters may also be created if the person was forced to harm others, as a way of containing the guilt of having to act in a way which feels more violent and animal than human. Complex trauma can leave even a non-dissociative person feeling "inhuman".:65,  Animal or animal-like alters should be accepted, and treated just like any other alter.:69, :133,:139 Animal alters can be taught that they are actually part of a human body, and can adapt. For example, a snake alter may be created when a child has arms and legs bound, and be tricked into believing that, like a snake, they do not have arms or legs.:69 Animal alters often have a definite gender and can present, and be accepted, as human, without the person necessarily being aware they are communicating with an animal alter or any alter at all.:55
These alters are pre-verbal (cannot yet express themselves with words). They may remain the same age, or grow older in age and begin to take on more responsibilities. :140 Their trauma memories consist primarily of emotions and bodily sensations.:223-224
Caretaking alters are a type of a protector, they help manage and care for other alters, and sometimes external people (for example children). :83 They are often motherly, and may be modeled on a real person. :61-62 Caretaking alters lack awareness of self-care and become exhausted easy; they only have a limited role and have little capacity for play, exploration or socializing. :83
Often nicknamed "littles" or "little ones" are a common type of alter. Several child alters exist in most people with DID. Child alters often talk in a child-like way, but unlike a biological child they can normally understand abstract concepts and long words. They are often found to hold memories of child abuse which occurred at around the age the child alter feels he/she is. :18 Some may have the speech or appearance of a very young child, the youngest being unable to talk, read or write. :18 Child alters may gradually age or may remain the same age. Some child parts may hold feelings of terror and pain, while others may be playful and fun-living and have only positive memories. :60 A child alter may also be an idealized representation of the "perfect child" from the "perfect" family, for example the "good boy". :18 Child alters should not be confused with the concept of having an "inner child", which applies to non-dissociative people. :129
Core personality. This term is now rarely used in scientific information. See Apparently Normal Part of the Personality.
Usually this is an alter hidden from the rest of the system, often in a memory of a trauma in which they felt they were being killed. The child who survives a near-death experience may develop a "dead alter" to contain this experience.:64 Alters can"t really die or be killed since the person"s brain is still alive, their feelings will still leak through into other alters. "Dead" alters can be revived.:35
Demon and demonic alters are a type of spirit and supernatural alter but are not actually supernatural beings and may result from spiritual abuse and an abuser who blames the child for the abuse.:170 In abusive groups, a young child can be severely traumatized in order for abusers to intentionally create an alter, and the alter can be tricked into believing they have been possessed by, and have become, a demon. Some survivors report being dressed to look like a "demon" with costumes and theatrical makeup, and being told to look in the mirror and told that they are a demon. Hallucinogenic drugs may also be used to cause supposedly "spiritual" experiences. :68,337 Some demon alters may be told they are animals. They may be very intimidating, with names such as Demon, Lucifer, Satan or Devil, however they should be able to engage with psychotherapy, and all alters should be accepted.:61 These "demonic" or "evil" alters may have the role of maintaining loyalty to the abusive cult which created them, in order to keep the whole person alive. They are often a form of protector known as a persecutor.:142 :337-338 These alters are usually hurt children who have been tricked into believing they are "evil", and may have been tricked or forced into harming others. With "patience, persistence and kindness" they can be allowed to choose a different role once the person is safe from abusers. Attempts to banish them using religious techniques such as "deliverance" or exorcism do not work permanently, can be harmful and may prolong any internal war between alters and preventing healing.:338-339, :170-171
For Christian perspectives on healing trauma, including experiences of people with Dissociative Identity Disorder and alters who understand themselves to be demons, see http://thoughtsfromj8.com/christian-resources-for-healing.
Alters may be disabled when the body is not, for example a blind or mute alter may be created in response to abusers instructions, e.g. "Don't talk", "You didn't see anything". These alters can regain their sight or hearing, for example, after working through the memories that caused their disabilities. :34-35
Like alters based on fictional characters or people known to the person with DID, these alters are internalized representations (introjects). They are rarely described by psychotherapists and psychiatrists, except when referring to survivors of ritual abuse. Examples in military/political abusive groups include child alters who believe they are Hitler, famous doctors, generals, or other military leaders. :337 There may be several alters who each believe they are the actual person they are based on, and are unaware of one another - e.g., several "Hitler" alters in the same person. :337 In ritual abuse with 'religious' beliefs, alters may believe they are Jesus, or supernatural beings like God or Satan. :325, 327.
Unsurprisingly, a person who has an alter claiming they are a famous person may be misdiagnosed as having Schizophrenia or a Psychotic Disorder, because claiming to be a famous person is considered a delusion. Psychotherapist Alison Miller gives the highly unusual example of a person who developed alters that were copies of Axl Rose and rest of Guns'N'Roses band - and was misdiagnosed with Schizophrenia as a result. :2 In DID/DDNOS, however, an alter can adapt their believe if presented with clear evidence that they are not that person, for example that Hitler is dead and the Nazis lost the war.:101 Note: Delusions can also exist in people with DID/DDNOS if they have a Psychotic Disorder or Schizophrenia as well.
Alters may be created which are internalized representations (introjects) of fictional characters. Some people with DID refer to alters based on fictional characters as fictives but this term is not used in literature on DID, which only rarely describes examples of them and doesn't classed as being a separate "type" of alter or given a particular name.,, Like any other alter, they can physically take control of the person's body. The characters that alter personalities are based on may come from sources like nursery rhymes, fairy tales, children's stories or books, music, and movies.:493 One good description of alters based on fictional characters comes from a case of DID in Turkey: a woman aged 45 with a severe abuse history was found to have Dissociative Identity Disorder, and two of her alters were based on the classic story Snow White:
"Two identities had been formed from childhood imaginary playmates: "Pamuk Prenses" (Snow White) and "Kraliçe" (The Queen). They both enjoyed parties at nights where the Queen looked after, protected and controlled the young "Pamuk Prenses" and enviously competed with her at the same time. Snow White danced and sang. When Snow White took control she saw her husband and children as "the relatives of that poor woman in the neighborhood" (Sad Halimé [another alter])... These identities had been formed at about the age of twelve; they knew the other personalities, but they saw themselves as distinct from all the others. :151
Some abusive groups/cults have been known to traumatize children in order to force them to create alters based on particular characters which suits the needs of the abusers. Ritual abuse survivors in particular report being forced to create alters based on many different fictional characters, including:
- characters from Lewis Carroll's story Alice in Wonderland, which has been made into several movies 
- An “everyday life” alter based on the character “Samantha” from an episode of the TV show "Bewitched" :523
- Charles Wallace and Meg (from Madeleine L'Engle's 1962 book A Wrinkle in Time) - as part of MK-Ultra ritual abuse:70:72
- Peter Munk (a character from a German fairytale) who is "unemotional, obedient, lacking in self-awareness" and motivated to avoid pain, reported in a German survivor of ritual abuse during the "cold war" :80
- Sleeping Beauty, who believed she was dreaming when actually working as a government agent (as part of MK-Ultra) :217,272
- Tinker-Belle (from Peter Pan), in a survivor of Monarch programming/ritual abuse :108-109
- The Wizard of Oz, including the scarecrow (who was told he had "no brain", was obedient and suggestible), the cowardly lion (who held the emotion of fear), tin man (who was told he had no heart - meaning no empathy, and as such was able to be a trained killer following someone else's orders):62
All alters may adapt and change over time, and some may even choose to take on the form of fictional characters if that serves a helpful purpose. Dr Colin Ross, a well known psychiatrist and Dissociative Disorders specialist, states that a group of demonic alter personalities in a survivor of Satanic Ritual Abuse chose to become Ewoks (from Star Wars) as part of healing.:153Fragment
Some alters are very limited in their role, for example they may only have a small number of emotions, hold particular isolated memories or have a very limited job. These 'partial' alters are sometimes known as fragments. :280 Fragments can either have a range of emotions but only a limited life history, or a more substantial life history but be unable to feel a range of emotions (for example, always sad, either angry or fearful). Special purpose fragments are even more limited, for example existing to carry out a very limited role and never acting beyond that. Memory fragments hold a very limited knowledge of an event, and only experiencing very limited emotions. :xii:xiii Several fragments together may hold a single event. :6, 143
This type of alter has the job of keeping traumatized alters from appearing. :58 They may also hold back memories or control which alters can take control of the body, and when. :54
The personality part/alter that "has executive control of the body for the greatest percentage of time during a given time period.":xiii A person with DID will have more than one host over their lifetime. :59 See Apparently Normal Part of the Personality.
This term covers many different kinds of alter who are not primarily responsible for everyday life, they often hold trauma memories. They often have been so separated from everyday life that they are unaware of the years that have passed and do not know that the body have physically grown up. :30 See Emotional Part of the Personality.
These alters are helper parts. They have extensive understanding of different alters and how they work together, and often help by explaining things to the therapist. :64 Also known as Managers or sometimes Inner Self-Helpers.
These alters believe may they are another person entirely, such as an abuser or a close relative. :34 They have the characteristics of another person, for example a paternal introject with the behaviors and views of a person's abusive father. :18 Introjects which are mimicking abusers are trying to "keep you inline" in order to protect you from external abusers.:33
"Introject" is a term used in general psychology to refer to taking on and internalizing the views and thoughts of others without reviewing them.:259 This is part of normal development in early childhood, these introjected parts/aspects of a person can be either healthy and helpful, or abusive. For example, an adult verbally abused as a child may have an introject which states "nobody likes you" or "it's a dog eat dog world" - both of these would negatively affects a person's likelihood of making friends. In people without DID/DDNOS, introjects will not be alters, but become incorporated (introjected) into their personality. Introjects can change with psychotherapy.
Alters may be soldiers of different ranks, or believe they are well known political leaders. These alters are often been created within abusive groups with a particular set of political/military or religious beliefs, the alters are indoctrinated to force them to take on the beliefs of the group.:61-63 They may have titles of military ranks, like generals, or names like Hitler. Groups which are known to have carried out ritual abuse using dissociation to create alters include the US government (e.g., MKUltra, which included many Nazi doctors operating on behalf of the CIA), neo-Nazi groups, and white supremacists including the Ku Klux Klan. :18, 54
See demon, demonic and 'evil' alters, for alters which are copies of actual people see introject.
Some alters may have a different gender to that of that body, for example a male alter in a physically female body. Opposite sex alters are usually more like a young girl's idea of how a boy would be an actual boy, or a young boy's idea of how a girl would be. Normally they have personality traits which associated with the gender of the opposite sex. A female alter in a male body may be very fearful or frightened, and a male alter in a female body may be very angry, feel physically strong, or be very brave. An alter may be have an opposite gender because of sexual abuse, for example a male alter does not have vagina, so will not fear being vaginally raped as the female body was. A female alter may be created in a male because that alter was forced to take on a female role in having sex with men. :34-35
Alters are the result of severe dissociation; they are "constructed by the 'logic' of dream or trance",:184, and can be strongly influenced by a person's culture.:294 As a result, they can take any form; some alters may not view themselves as human, and may either feel (or fully believe) that they are not part of a human being. They may view themselves as having a different physical form (or no physical form at all, for example a spiritual being), this is recognized within the DSM-5's description of DID. :294 Prolonged and severe interpersonal trauma can leave a person feeling "no longer human", and has been reported in people with Complex PTSD for example as a result of being a prisoner in a concentration camp, or severe child abuse. :65,  Given the trauma history of the vast majority of people with Dissociative Identity Disorder and DDNOS, it is unsurprising that parts of the mind may have taken on a nonhuman identity. Some examples include alters that identify as animals, demonic or 'evil' alters, spirits, ghosts or spiritual beings,, mythical figures,:294,:184 robots or machines, or even inanimate objects :47. Some people with DID or DDNOS refer to such alters collectively as "otherkin", although the word otherkin can have different meanings, including meanings not relevant to Dissociative Disorders.
Alters which identify as inanimate objects are a type of nonhuman alter, for example a tree.:80 Alters can also be hidden inside animate objects, for example inside natural-looking structures in the inner world, e.g., mountains, trees, lakes or rivers. :49
A common type of alter, often acts in a harmful way but there is a protective logic behind a persecutor's actions. :17-19 Persecutors often have a distorted view of reality, and may disrupt therapy or intentionally injure the person's body, for example to punish child alters for disclosing abuse that has been kept secret. All alters "should be treated with equal kindness," despite their behaviors, and persecutors are often seen as "misguided protectors" which can be negotiated with.:41,  Some persecutors may threaten to "kill off" the ANP (host) and appear to have no positive or protective intentions, however these can still be engaged with.:95 Some persecutors may be introjects of abusers. Download Therapeutic alliance with abuser alters in DID for more information on responding to a persecutor.
Protector alters are common, there are three main types: 'fight' parts, persecutors and caretakers. The 'fight' parts and persecutors are types of EP which have defensive intentions, despite their often self-destructive behaviors such as self-injury or eating disorder behaviors.:82-83 The term 'fight' does not necessarily refer to violence, but to the 'fight' reaction present in PTSD, which often involves verbal aggression.:143 A diagnosis of DDNOS or Dissociative Identity Disorder is not associated with crime or "wild aggression".  Therapist Jo Ringrose, who has considerable experience of working with alter identities, states that violent alters exist, but has never met one. :8
Protector alters try to manage rage and anger, and avoid feelings of hurt, fear or shame. They focus on perceived threats, and find dependence, emotional needs and close relationships (attachment) threatening. Protectors may view themselves as a very tough child or teenager, a powerful animal, or a physically strong, adult male. They can act internally, or show external hostility, e.g., telling a therapist that other alters don't need them and warning the therapist to leave them all alone.
Defensive "acting out" may be directed at a therapist or others close to the person; the ANP may have no behavioral control or memory of it. However, the "whole person" (all alters collectively) should still be held responsible for the behavior of all parts.:132 A protector may follow an alter that is "needy and searching desperately for attachment" in order to protect it.:87
Internal perceived threats may include the crying and dependency needs of a traumatized child part, which an internal persecutor may silence with rage or self-harm. :82-83 Protector parts may see the partner of an ANP (host) as a threat, for example the partner initiating sex may cause a switch to a protector alter, who perceives it as an attempt to rape, and fights off the partner. :74 Communication and negotiation can improve safety, and no attempts should be made to "get rid" of any alters.:132-133, :139
“With DID patients, if they feel hostility or aggression they take it out on themselves with self-harm... They’re self-destructive and repeatedly suicidal, more so than any other psychological disorder. So that's what's typical – not this wild aggression, or stalking women..." —Dr Bethany Brand 
Some alters have psychosis or psychotic symptoms. However, many symptoms which appear psychotic are not. For example, visual flashbacks may be mistaken for hallucinations, and strange body sensations (body memories) which are physical flashbacks of past trauma can be mistaken for tactile hallucinations. :64 Hearing "voices" is a common experience in people with DID/DDNOS, the "voices" are alters trying to talk, and occasionally may come from outside the person's head rather than inside, which is more common. "Thought snatching" (taking away your thoughts) can be caused by the actions of alters. Beliefs caused by trauma can be mistaken for paranoia, for example a person may be told that a "bug" has been implanted by abusers to record any dislosures they make. Working through the memory of the trauma will resolve the paranoia that it caused. :129
Some people who have been abused within ritually abusive groups may have alters who are trained (programmed) to produce psychotic-like symptoms under certain circumstances.:142 It is possible to have an alter with a psychotic disorder, or to have schizophrenia as well as DID/DDNOS. :291-307 This appears to be relatively rare. Schizophrenia is a common misdiagnosis for people with Dissociative Identity Disorder, although many people with DID/DDNOS believe they are going "crazy" they do not have a break with reality.:58-59 Abusive groups are known to have created alters who carry out "jobs" which make a person appear either "crazy" or learning disabled, for example scrambling or garbling words and numbers so they cannot be understood, hearing high pitched sounds and feeling "lost in a maze" in the back of your head, making your mind go foggy or misty or being spatially confused and unsure what the truth is.:78, 80-81 Anti-psychotic medication will not "remove" alters but can make the communication needed to heal more difficult.:129
Alters who believe they are robots or machines, and have no understanding of emotions, have been reported in survivors of ritual abuse. These alters were told they were robots or machines, and were not allowed to feel any emotions, were trained to follow instructions and not to think, and may have been made to believe that they cannot move.:68 If a large number of similar robot parts exist, it is more effective for them to agree to fuse (integrate together permanently) rather than repeating the same therapy with each. Robot and machine parts are actually part of a person, and can be helped to feel more human, and to learn how to think for themselves, rather than just responding to the instructions past abusers gave. :142-143
Sexual alters may be created to handle sexual abuse and rape, and to keep that knowledge away from other parts. One alter or group of alters may handle sexual abuse from men or boys, while others are created to handle sexual abuse and rapes from women or girls. :77
A shell alter is an Apparently Normal Part (host alter/front person) which handles daily life and is designed to hide the existence of other alters from the outside world. :33 Shell alters do not exist in DID, they only exist in one form of DDNOS (now renamed to Other Specified Dissociative Disorder). The apparently normal part (ANP) is a shell through whom the inside parts/alters act. The inside parts can come near the surface, temporarily blending with the ANP. The inner parts are not regarded as separate, distinct states although amnesia may exist between them. :9, :5 If DDNOS is caused by ritual abuse and mind control, the shell alter is not supposed to know about the others.:5
These types of alters are referred to directly in the DSM-5 diagnostic manual, underneath the diagnostic criteria for Dissociative Identity Disorder. Some people have alters which are all spirits, ghosts or supernatural beings such as angels or genies. These are regarded as possession-form identities, if a person is consciously aware of the actions of the alter then the person may describe themselves as feeling "possessed" by an outside person, spirit, deity (god), demon, or a "ghost", for example of a person known to them who has died. :292 Possession-form alters are not part of normal cultural possession experiences, they are involuntary, recurrent and distressing. :294 Animal alters are also common in this form of dissociation.:293 People can also have one or more of this type of alter along with other types, for example child alters or protectors.
Alters who believe they are spiritual or supernatural beings should be treated in the same way as any other type of alter identity, with psychotherapy (talking therapy). Exorcisms are known to be harmful and ineffective in treating complex dissociative disorders, and attempts should not be made to "get rid" of alters. Instead they should be understood as a way of coping with traumatic life experiences. :170-171
An alter may have another dissociated part inside, which has a different role or function. :141
A common type of alter.:79 If somone with Dissociative Identity Disorder or DDNOS is suddenly suicidal, this may be due to the influence of a suicidal alter, although the ANP (host) themselves may be feeling suicidal.:75, 306 According to the DSM-5 psychiatric manual, over 70% of out-patients with DID attempt suicide and multiple attempts are common. Amnesia can make it difficult to assess the suicide risk, and there may be amnesia for a suicide attempt. :295 Some alters may be unaware that they share the same body as the ANP, and believe that killing off the ANP or others will not harm them; this increases the suicide risk further.:132, 140 See persecutor for alters who are threatening to kill the ANP (host).
See Negotiating with alters
Teenaged or adolescent alters may occur in people who had significant trauma during those years, or they may be child alters who have grown older.:18
Twin alters are two alters of the same age who are normally opposites of each other in views and behaviors. Twin child alters are common, for example one may love the abuser, be eager to please and have only positive views towards him/her, and another may hold angry and rejecting views towards the abuser. :61
Number of Alters
This varies widely between people, the minimum needed for diagnosis is two different dissociated (disconnected) parts/identities, e.g., one alter plus a host or main identity, or two alters without a host identity.
In 1984, influential research found approximately half of people with DID had ten alters or less, and half had eleven or more. The DSM-IV (published in 1994) repeated this, adding that "[t]he number of identities reported ranges from 2 to more than 100", and stating that adult women averaged 15 or more alters, and men had an average of 8.:485-486 Howell (2011) states "[t]he number of parts [alter personalities] in a DID system usually ranges in the teens. In some cases ... there are also polyfragmented multiples who have many, many parts—perhaps close to a hundred or more parts".:58 In recent years there has been little focus on reporting the number or characteristics of alters in clinical research. The number of alters is not mentioned in the DSM-5 (published in 2013). The number of alters a person with DID is aware of often increases during treatment; one study, in 1988, found an average of between 2 and 4 identities at diagnosis, with between 13 and 15 emerging during the course of treatment., This does not mean that treatment in some way caused new alters to be created. Instead it is understood that existing alters feel able to emerge from hiding, they may emerge naturally during psychotherapy if there is something they wish to communicate or if something triggers them. 
Polyfragmented Dissociative Identity Disorder or DDNOS
A person with DID or DDNOS is said to be polyfragmented if they have a very large number of alters or parts. Some professionals refer to people with over 100 alters/parts as polyfragmented multiples,, although others use the term polyfragmented to refer to "dozens" of alters.,:4,:58 This large number typically include many personality fragments. Several different parts may use the same name, or have no name.:16 Alters or parts may be arranged in many different ways internally, e.g., hidden behind other parts, or within a hierarchy of parts arranged in layers or levels.:49 A large number of alters and fragments results in less obvious physical signs of switching. :27
Trauma which is "severe and long-lasting" produces the most splitting, creating large numbers of fragments and alters. :19 Such large numbers are likely to be caused by highly organized abuse, e.g., cult abuse, ritual abuse, pedophile rings, or other form of extreme, sadistic abuse which extends over long periods of time and often involves multiple perpetrators. :4, :133 A person with large numbers of fragments and less active alters can heal at least some of them fairly quickly. This is because many of them will have similar roles and functions, this allows them to fuse together (permanently integrate) relatively easily. Kluft and Fine (1993) describe how a patient who had been severely traumatized had a protector alter for each of the 300 fragments holding her memories and pain. These protectors were all carrying out the same role, and had the same information as each other, so they decided to fuse together, into just one. The fragments holding the memories and pain needed to spend time processing the most significant traumas first, and gradually fused into groups of up to 10 at once.:126 Polyfragmented DID was previously called Complex Multiple Personality Disorder (Complex MPD),:306 but has never been a separate diagnosis. People who have publicly described their experiences of being polyfragmented include artist Kim Noble,:xii and Truddi Chase, author of When Rabbit Howls.
How alters are created
Alter identities are created to manage either overwhelming trauma, or changes in everyday life that cannot be managed by any existing identites. Some people have been able to recall and describe the child abuse which directly caused a particular alter. The child's beliefs and culture are known to influence spontaneously created alters, for example a Native American man described having animal and spirit alters which were created by a mixture of starvation, severe beatings and hallucinogenic herbs or drugs. His wolf alter was created after beatings for failing to communicate with the "wolf spirit", the wolf alter took on the characteristics he attitrubed to wolves: widsom, cunning and wolf-like behaviors. The wolf alter both allowed for the trauma to be handled and was able to use its characteristics to diagnose illness and manage complex life situations.  Additional alters can also be created by traumatization in adulthood if the person already has a complex dissociative disorder. For example, an alter created to handle sexual abuse may be unable to cope with increasing levels of abuse, and may create other alters to handle some of that abuse. :77
Organized perpetrator groups may intentionally create alters and train them to do particular jobs. In ritual abuse, abusers intentionally severely abuse the child until an alter develops. :54 If the alter refuses to comply with the "job" or role they are given then the abuse continues until another alter is formed, who then faces the same dilemma. Eventually an alter must agree to ensure survival. :54
Co-conciousness and Amnesia
Co-onsciousness involves two or more alters each being aware of the other's presence, and having an on-going memory of a situation or particular period of time. One is normally in "executive control" of the person's body, while another is able to watch, listen and think about what is happening. The alters who are co-conscious with one another will not necessarily behave as one. Co-consciousness is an important way of reducing amnesia and improving co-operation and functioning in everyday life. A person with continual co-consciousness will not "lose time" in the present, but may meet the diagnostic criteria for Dissociative Identity Disorder because they still have some amnesia for past events. If there is no amnesia for past or present events, then a person with alters is likely to fit the criteria for Other Specified Dissociative Disorder (formerly DDNOS)., 
Do Alters exist in DDNOS?
Dissociative Disorder Not Otherwise Specified (DDNOS) has been renamed to Other Specified Dissociative Disorder in the DSM-5, and includes many different presentations of complex dissociative symptoms, two of which are very similar to DID. One form of DDNOS has alter identities but there is no amnesia, either for the past or for events in the present. This was known as DDNOS-1b in the DSM-IV, :409, and is one of the two possible forms of OSDD-1 in the DSM-5. The research on DDNOS consistently states that Dissociative Identity Disorder may first appear as DDNOS because there is not quite enough evidence to be sure of a DID diagnosis, so some people initially classed as DDNOS will later be classed as DID. The same treatment guidelines apply to both forms of DDNOS-1 and to DID.
The presence of alters alone is not quite enough for a person to be diagnosed with a mental "disorder". For a dissociative disorder to be diagnosed the person must have either clinically significant distress, or impaired functioning in a major area of life. [1,2] This means that it is possible to be mentally healthy and a multiple, this is referred to as "healthy multiplicity".
Some people incorrectly assume that the goal of treatment for Dissociative Identity Disorder (and similar forms of DDNOS) is to either remove "alters" or to fuse into a single identity. This is not correct; removing alters is not possible and fusing them into a single identity is not necessary although some alters do choose this. There are different options in treatment, and the majority people do not fully integrate, only around a third do.  Psychotherapist Dr Alison Miller states that multiplicity is called a "disorder" in psychiatry but it is actually a "valuable, creative asset" which makes a person "well adapted to living with ongoing trauma".  Miller states that multiplicity "is not an inferior way of being" and has some advantages. Advantages may include having some alters which do not have the distraction of emotions or managing everyday life, so, they are able to have a single focus and do amazing things are like special being able to memorize large amounts of information (savant abilities). Some multiples whose alter personalities are extremely cooperative prefer to stay as a community of coordinated alters rather than seeking integration into a single identity.
Dr Colin Ross, a well known expert on treating Dissociative Disorders, states that the intrusive actions of "part selves" (alters) is not the actual problem, and recognizes healthy multiplicity as possible.
"the problem in MPD is not the intrusion of part selves as such, it is with the degree of amnesia, conflict, self-destruction, and dysfunction in the psyche. The problem is not the multiplicity, it is the degree of pathological dissociation. In MPD the part selves are personified to an abnormal degree. There is a big difference between someone with active classical MPD, and an individual with healthy multiplicity."