Possibly the most controversial of the dissociative disorders is dissociative identity disorder, which was previously known as

The correct answer is multiple personality disorder.
The usual cause of a dissociative identity disorder (DID) is some kind of a childhood trauma - such as childhood abuse, war, or health issues. This results in DID, which is a disorder that has to do with individuals creating two or more different personality states, none of which are usually aware of the other ones' existence.