a big fish

a big fish

An important, successful, or influential person. Meeting a big fish like the company's CEO can be quite an intimidating experience for an intern. I'd rather be a big fish in a small pond than move to New York City and be a nobody!
See also: big, fish
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

a big fish

COMMON If you call someone a big fish, you mean that they are important or powerful. The four who were arrested here last September were described as really big fish by the U.S. Drug Enforcement Agency.
See also: big, fish
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012

a big ˈfish (in a little/small pond)

an important person but only in a small community, group, etc: I would rather stay here in the village and be a big fish in a little pond than go to the city where no one knows me.
See also: big, fish
Farlex Partner Idioms Dictionary © Farlex 2017

big fish

n. the boss; the leader. (Underworld.) We took in the little guys, but the big fish got away.
See also: big, fish
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.
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References in classic literature ?
"Does a big fish ever break the line and get away?" inquired the politician, with respectful interest.
"I remember," he said, "and about how a big fish might break the line and get away."
The idea of finding himself in so lonesome a spot made him so sad that he was about to cry, but just then he saw a big Fish swimming near-by, with his head far out of the water.