king of the castle

noun2

1. •
   A children's game in which one player is located on something elevated and other players attempt to take his or her place.

   • [A] throng of children came pouring from school. […] [T]hey were storming the sand-heap, pelting a king of the castle, who pelted back with handfuls. — 1912
2. •
   A person who assumes a position of greater importance, authority, or prominence than others.