"The Minds of Billy Milligan" is a non-fiction book by Daniel Keyes that explores the life of Billy Milligan, a man diagnosed with dissociative identity disorder (formerly known as multiple personality disorder). Milligan was arrested in the late 1970s for a series of crimes, including robbery and rape, but his defense claimed he was not responsible due to his multiple identities. The book details Milligan's 24 distinct personalities, each with its own traits and memories. It examines the psychological implications of his condition and raises questions about the nature of identity and accountability in the context of mental illness.