From Longman Dictionary of Contemporary Englishbig cheeseˌbig ˈcheese noun [countable] informal IMPORTANTan important and powerful person in an organization – used humorously
Examples from the Corpus
big cheese• Evidently he was considered a big cheese here, and was greeted by everyone.• One of the big cheeses from NASA gave a speech.Origin big cheese (1900-2000) cheese probably from Urdu chiz “thing”, from Persian 