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. (June 2010)
An alter ego (Latin, "the other I") is a second self, which is believed to be distinct from a person's normal or true original personality. A person who has an alter ego is said to lead a double life. The term appeared in common usage in the early 19th century when dissociative identity disorder was first described by psychologists. Cicero coined the term as part of his philosophical construct in 1st century Rome, but he described it as "a second self, a trusted friend".
A distinct meaning of alter ego is found in literary analysis used when referring to fictional literature and other narrative forms, describing a key character in a story who is perceived to be intentionally representative of the work's author (or creator), by virtue of oblique similarities, in terms of psychology, behavior, speech, or thoughts, often used to convey the author's own thoughts. The term is also sometimes, but less frequently, used to designate a hypothetical "twin" or "best friend" to a character in a story. Similarly, the term alter ego may be applied to the role or persona taken on by an actor or by other types of performers.
The existence of "another self" was first recognized in the 1730s. Anton Mesmer used hypnosis to separate the alter ego. These experiments showed a behavior pattern that was distinct from the personality of the individual when he was in the waking state compared with when he was under hypnosis. Another character had developed in the altered state of consciousness but in the same body.
Alter ego is also used to refer to the different behaviors any person may display in certain situations. Related concepts include avatar, doppelgänger, impersonator, and dissociative identity disorder (DID).