Dissociative identity disorder
Even though DID is a very rare, there are a lot of books, plays and movies about people with DID.  In 1886 Robert Louis Stevenson published the short book The Strange Case of Dr. Jekyll and Mr. Hyde which was very popular.  People later thought that Dr. Jekyll and Mr. Hyde were examples of someone with DID.  The Three Faces Of Eve was a movie made in 1957 about a woman with DID.  Sybil, a popular book about a woman with DID, was published in 1973.  It was made into a movie in 1976, and a second time in 2007.  A survey done in 2001 of American and Canadian psychiatrists found that there was a lot of disagreement and skepticism about diagnosing DID and if the diagnosis was based on enough good quality science.