king of the hill

Short definition from Wiktionary

Noun

1. 1
   A children's game in which one player stands on top of a hill or other location atop an incline, and attempts to repel other players whose goal is to capture his position.
2. 2
   The player in this game who stands atop the hill.
3. 3
   A person who has achieved a measure of success and is considered to be a leader in his field.