top gun; big cheese; top dog
Slangy loanword for a top performer, ace, or the most important person in a group. Often used in business, sports, or competitive contexts.
He's the top gun in the sales department.
That player is performing as the team's top gun.
Variant with interpunct; less common in running text.
Borrowed from English 'top gun', originally referring to an expert marksman or fighter pilot, and popularized by the 1986 film.