Dissociative Identity Disorder (DID) or Multiple Personality Disorder (MPD) is a mental state characterized by two or more identities or personalities that control a person's behavior, accompanied by memory impairment.
We won't get into great details when it comes to psychological definitions, nor symptoms, We'll try to focus exclusively on movies and the way this state has been used to create fascinating plot twists and movie characters. It has been used ever since the first adaptations of "The Strange Case of Dr Jekyll and Mr Hyde", but especially in the last few decades.
Not many movies manage to handle this plot device in a believable manner, but here is a short list of those which succeeded to do a considerably good job. Obviously, the title itself is a major spoiler, we will try not to give away much more, but still, proceed at your own risk.
