ALTER EGO /ˈɔltərˈigoʊ,ˌɛgoʊ,
1. a second self, a perfect substitute or deputy, his adviser acts as, his Alter ego during his absence.
2. an inseparable friend
3. another aspect of one’s self

The concept appears frequently in popular fiction, but also in comic books or cartoons, to indicate the secret identity,
of a superhero