This document discusses Dissociative Identity Disorder (DID), formerly known as Multiple Personality Disorder. It describes the causes and symptoms of DID, which include severe trauma, neglect, distinct identities or personality states, and extensive memory loss. The document also summarizes the plot of the 2003 movie "Identity", in which strangers are murdered one by one at a hotel, and one character is revealed to have DID through conversations with his different personalities.