An alter ego (Latin, "the other I") is a second self, a second personality or persona within a person. The term is commonly used in literature analysis and comparison to describe characters who are psychologically identical.
The term and concept also frequently appear in popular fiction, such as in comic books, for the secret identity of a superhero, vigilante, or crimefighter. Related concepts include avatar, doppelgänger, impersonator, and split personality. It was created in the early 1800's when people first discovered schizophrenia.