King Boo is a character from the Mario franchise who first appeared in Luigi's Mansion. Synonyms for the term "King Boo" include "the ruler of all Boos," "Boo King," "Royal Boo," "Majestic Boo," "Supreme Boo," and "Emperor Boo." These synonyms all emphasize King Boo's position as a powerful and authoritative figure among the Boo species. King Boo is known for his villainous tendencies and his ambition to conquer the Mushroom Kingdom. His status as a king makes him a formidable foe for Mario and Luigi to face in their adventures. Despite his intimidating title, King Boo is a popular character among fans of the Mario franchise.