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An alter ego (Latin, "the other I") is a second self, a second personality or persona within a person. It was coined in the early nineteenth century when schizophrenia was first described by early psychologists.
The term alter ego is commonly used in literature analysis and comparison to describe characters who are psychologically identical, or sometimes to describe a character as an alter ego of the author, a fictional character whose behavior, speech or thoughts intentionally represent those of the author.
The characters Doctor Jekyll and Mister Hyde in Robert Louis Stevenson's thriller Strange Case of Dr Jekyll and Mr Hyde represent an exploration of the concept that good and evil exist within one person, constantly at war. Edward Hyde literally represents the doctor's other self, a psychopathic being unrestrained by the conventions of civilized society, who shares a body with the doctor.
The term and concept also frequently appear in popular fiction, such as in comic books, for the secret identity of a superhero, vigilante, crime fighter or villain. Related concepts include avatar, doppelgĂ¤nger, impersonator, and split personality.