King Boo

King Boo is a recurring character in the Mario series. He is the leader of all the Boos. He can easily be identified by the crown on his head, and his larger size compared to most Boos.

Luigi's Mansion
King Boo has a prominent role in Luigi's Mansion. He is the final boss, and the cause of all of Professor Elvin Gadd's troubles (it is later found out that King Boo released all the ghost boss portraits, as one of the portraits was of Boolossus). King Boo created a mansion next to E.Gadd's lab where the portrait ghosts roam freely. Luigi later finds out that King Boo has captured Mario inside of a golden portrait, and must travel to the furthest point of the Mansion (after defeating a good chunk of Boos).

In the final confrontation, King Boo hides within a giant Bowser suit and is invincible until Luigi shoots a spike bomb at him. "Bowser's" head pops off, and King Boo pops out, and sucks him up. He has a whopping 500HP.

Once Luigi sucks him up, King Boo is turned into a portrait, and Mario returned from inside the portrait.

Mario Kart: Double Dash!!
King Boo appears as an unlockable playable character, paired alongside Petey Piranha. His special power is the ability to copy any other character's special power. He is a heavy-set character.

Mario Kart Wii
King Boo, once again, appears as an unlockable playable character.

Mario Superstar Baseball
King Boo appears as a starter playable character. He appears on Wario's team, and has terrible chemistry with Luigi. He is a strong hitter, and a decent pitcher, but a poor runner.