King Boo is a character from the Mario video game series, known for being the leader of the Boo ghosts. He first appeared in Super Mario 64 and has since become a recurring antagonist in various games. King Boo is characterized by his large, round body, a crown, and a mischievous grin. In the games, King Boo often challenges Mario and his friends, using his ghostly powers to create obstacles and traps. He is typically found in haunted locations, such as haunted mansions or ghost houses. Players must defeat him to progress through the game or to complete specific objectives.