big hitter
From Longman Dictionary of Contemporary Englishbig hitterˌbig ˈhitter noun [countable] someone who is very important and successful and who has a lot of influence one of the big hitters of the Conservative PartyFrom Longman Business Dictionarybig hitterˌbig ˈhitter noun [countable] informal journalism a person or organization with a lot of influence or powerSYNheavy hitter