King Boo

"...I will fight you like a true boo!"

- King Boo

King Boo is the king of all Boos as his name suggests. He is a disturbing individual who has a particular contempt for scaring. He is also the arch-nemesis of Luigi, and as such serves as the main antagonist for the Luigi's Mansion sub-series.

Luigi's Mansion
He made his first major appearance in the game Luigi's Mansion. He is angry with the Mario Brothers for causing them so much trouble in the past, so he designs a plot to get rid of them both. He sends Luigi a note telling him he has won a mansion... in a contest that he didn't enter. Luigi calls Mario and tells him the good news, asking him to go there and meet him so they can celebrate. However, when Luigi arrives, Mario is nowhere to be seen, and the mansion is infested with ghosts.

Later in the game, we find King Boo staring at a painting with Mario trapped inside. Also, we find out that he was the one who created the mansion and released all the ghosts within it. At the end of the game, Luigi fights what appears to be Bowser, revived from his previous (unseen) defeat by King Boo, but is really King Boo in a Bowser costume. Luigi defeats King Boo and sucks him into the Poltergust, and later turns him into a portrait with the Portrificationizer.

Other Appearances
He is later released from his portrait by Bowser Jr., where he fought Mario at the casino of Sirena Beach in Super Mario Sunshine. He uses a slot machine in battle, and Mario defeats him by throwing spicy peppers at his tongue, setting it on fire, and then throwing fruits at him. After three hits, King Boo is destroyed.

However, he is revived by Bowser at least once more, and appears as the third boss in Super Princess Peach, at Shriek Mansion. He is shown to have a weakness for extremely bright lights, as when Peach uses Rage to light all the torches in the room, King Boo takes damage. Once this happens five times, King Boo is destroyed.

He also appears in spinoffs such as Mario Kart: Double Dash!, in which he is an unlockable and playable character.

Luigi's Mansion: Dark Moon
King Boo reappears in the sequel to Luigi's Mansion on the 3DS and seeks revenge against Luigi for his imprisonment. At same point in this canon, E. Gadd lost the painting at a yard sale (presumably leading to his release in Super Mario Sunshine). King Boo initiates the events of the game by destroying the Dark Moon, a purple crescent-shaped artifact that keeps the ghosts of Evershade Valley in a docile state. Shattering the Dark Moon into pieces, King Boo incites the ghosts to turn on E. Gadd which leads to his summoning of Luigi for help.

Eventually, King Boo reveals himself to Luigi after intercepting E. Gadd's teleportation and entraps Luigi in an alternate dimension. There, King Boo demands the Dark Moon pieces from Luigi so that he may conquer the Mushroom Kingdom with a spectral army in exchange for releasing Mario, once again trapped in a painting. Luigi naturally refuses and the battle ensues, with Luigi triumphant. However, after catching King Boo in the Poltergust 5000, no specific mention of King Boo's fate is ever brought up. (This may have been set before Super Mario Sunshine, however)

Characteristics
Besides possessing the abilities of other Boos, including the ability to teleport, King Boo has a number of other magical powers. Notably, it should be mentioned that King Boo's power increases when he is in the presence of other Boos. For example, King Boo had the power to blow Luigi to the Foyer only when enough Boos were in the mansion. King Boo also has the incredible power to materialize things out of thin air, including highly detailed mansions. He has also shown the ability to create Boos, bubbles, and blue fire, which he spits out of his mouth.

Although King Boo is a lot larger than regular Boos, he is not the largest of the Boos. However, even gigantic Boos like Boolossus follow his leadership, despite their superior size. This is likely because he is the most intelligent and the most powerful of the Boos. King Boo seems to have a passion for gambling, as the entrance to each wing in Luigi's Mansion was modeled after a playing card suit (spade, club, heart, and diamond). The Boo leader also lived in a casino during the events of Super Mario Sunshine, using a slot machine to produce random events in battle.

King Boo has an extreme dislike for the Mario Bros., due to their constant intervention in the plans of the Boo leader and others of his kind. He shows a bit of a snarky side in Dark Moon when he confronts Luigi with "Remember when you trapped me for all eternity in a painting? Good times." Lastly, King Boo has a distinct cackle, which is significantly lower in pitch than other Boos.

Trivia

 * King Boo's quote, "I don't plan to give up my favorite decoration. I like Mario where he is." is a quote derived from Star Wars VI: Return of the Jedi, when Jabba the Hutt said, "I don't plan to give up my favorite decoration. I like Captain Solo where he is."
 * In his first three mainstream appearances, King Boo fights a different protagonist. Luigi fights King Boo in Luigi's Mansion, Mario fights him in Super Mario Sunshine, and Peach fights him in Super Princess Peach. However, as of Luigi's Mansion: Dark Moon, Luigi has fought him twice.
 * In the English version of Super Mario 64 DS, King Boo was mistranslated into Big Boo.