second self

American  

noun

1. one who associates so closely with a given person as to assume that person's mode of behavior, personality, beliefs, etc.

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Etymology

Origin of second self

First recorded in 1580–90

Example Sentences

Chance didn't live to meet his second self, but when the calf was born, Fisher christened him Second Chance, convinced he was the same animal.

From Salon

He called autumn, “Death’s second self, that seals up all in rest.”

From Los Angeles Times

The idea of confronting an unknown second self is full of rich, uncanny potential — there’s a literary tradition going back at least to Edgar Allan Poe — but “Gemini Man” squanders it, along with what might have been two interesting performances.

From New York Times

Sometimes the child felt a second self inside, a watchful and small and crouching thing.

From The New Yorker

But the edges of the second self were becoming vague and one day it would vanish altogether.

From The New Yorker