king of the castle

Noun

king of the castle (usually uncountable, plural kings of the castle or kings of the castles)

1. (usually) 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, Arthur Quiller-Couch, chapter 2, in Hocken and Hunken

   Synonyms:

   king of the hill

2. (broadly, derogatory, idiomatic, sarcastic, sometimes, usually) A person who assumes a position of greater importance, authority, or prominence than others.
   • Mr. Matthews, usually nonjudgmental when writing about O'Connor's domestic relations, can't resist calling him "the king of the castle, the smug possessor of a bevy of three fine women absolutely de-voted to him."1983 April 30, Deirdre Bair, "Enmity, Torment, Adversity" (review of Voices: A Life of Frank O'Connor by James Matthews), New York Times (retrieved 3 Jan 2019)
   • [A] onetime classmate in Kumamoto said, "I think Matsumoto is trying to create a closed society like the school for the blind he went to. He is trying to create a society separate from ordinary society in which he can become king of the castle."1995 April 30, James Walsh, “Shoko Asahara: The Making of a Messiah”, in Time, retrieved 03 Jan 2019

   Synonyms:

   king of the hill, King of the Jungle, baron, big cheese, big enchilada, big gun, big kahuna, big man, big name, big noise