Kingfin

Kingfin is a boss in  Super Mario Galaxy. This boss is a giant skeleton fish, living in the Bonefin Galaxy. To defeat it, Mario must take shells, and throw it at an "X" mark on Kingfin's interior. After being hit several times, KingFin will summon a group of robotic fish to help him in battle.

Trivia
Kingfins's name is a pun on the word "kingpin," which means: "The most important person in an undertaking or organization".