Dissociative Identity Disorder (D.I.D) [formally known as Multiple Personality Disorder] is a severe form of complex post traumatic stress disorder (C-PTSD), developed in children who have experienced long term abuse/neglect, coupled with unstable relationships with primary caregivers, and obtained the ability to disassociate to a high level at a young age to cope with their ongoing trauma.

Alternate Personalities (Alters) are formed to isolate and compartmentalize traumatic memories, and/or take on different roles in the Host's life in order to function normally in everyday living.

Each system of alters (i.e. other people with D.I.D) may be unique in structure and themes, depending on their own experiences and personal ways of coping with their specific traumas.