‘Alter ego’ means another side of oneself, or a second self. It can also be used to refer to a close or trusted friend.
The meaning of ‘alter ego’ in English is ‘alternative personality.’ This Latin term was first used in English in the early 16th century (circa 1530.)
‘Alter ego’ is a popular figure of everyday speech, so common that some people may not even be aware that it is actually a Latin term. It is rarely used incorrectly, although the use of the term to mean ‘close friend’ is often forgotten.
Alter ego should be used to describe another persona of somebody, usually one that the person in question has created for themselves. Examples of use of the term in a sentence include:
‘Beyonce’s alter ego is Sasha Fierce.’
‘His fiercer, more confident alter ego seemed to appear when he was performing on stage.’
Or when referring to a close friend:
‘She and her alter ego were inseparable.’
‘You never saw him without his alter ego Edgar.’