King Boo is a character introduced in Luigi's Mansion. He is both the main antagonist and arch-nemesis of Luigi in the Luigi's Mansion series, which also includes him as the leader of the Boos and ghosts. King Boo is allied with Bowser, whom he has assisted on various occasions. He has captured Mario in every game of the Luigi's Mansion series, prompting Luigi to rescue him. King Boo's main powers include materializing objects and spitting fire, though King Boo's power is often directly proportional to the number of Boos in his vicinity.