King Boo

King Boo first appeared in Luigi's Mansion, as the final boss. King Boo kidnaps Mario, and it's up to Luigi to rescue Mario with the help of the Poltergust 3000, a vacuum he recieves that is use to suck up ghosts. King Boo also makes an appearance in Super Mario Sunshine and Super Mario 64 DS as a boss (though his name was Big Boo, it is either a mistake, or his full name), and is a playable character in Mario Kart: Double Dash!! and Mario Superstar Baseball.