MPD

Dissociative identity disorder (previously known as multiple personality disorder) is a fairly common effect of severe trauma during early childhood, usually extreme, repetitive physical, sexual, and/or emotional abuse.
What is dissociative identity disorder?

Most of us have experienced mild dissociation, which is like daydreaming or getting lost in the moment while working on a project. However, dissociative identity disorder is a severe form of dissociation, a mental process, which produces a lack of connection in a person's thoughts, memories, feelings, actions, or sense of identity. Dissociative identity disorder is thought to stem from trauma experienced by the person with the disorder. The dissociative aspect is thought to be a coping mechanism -- the person literally dissociates himself from a situation or experience that's too violent, traumatic, or painful to assimilate with his conscious self.