alter ego

 
Pronunciation: /ˌaltər ˈɛgəʊ, ˌɒlt-, ˈiːg-/

noun (plural alter egos)

  • a person’s secondary or alternative personality: in the flesh she is a million miles from her photographic alter ego
  • an intimate and trusted friend.

Origin:

mid 16th century: Latin, 'other self'