King Boo

King Boo is the leader of the Boos and ghosts, ruler of the Paranormal Dimension, the main antagonist of the Luigi's Mansion series, and the arch-enemy of Luigi. He is also an ally of Bowser, who has aided him in his various schemes. He is more than capable of devising and enacting villainous plans by himself, including his capture and imprisonment of Mario. Although not the biggest Boo, King Boo has abilities that far surpass that of the average ghost; he wields a number of impressive magical abilities, including the ability to materialize objects. King Boo's magical power is directly proportional to the number of Boos in his vicinity.

In When the Cold Breeze Blows Away, he is the major antagonist serving for Undead Alliance that he went into against the entire of Mushroom Kingdom and Grand Alliance.