|Living Town||Luigi's Mansion|
|Vulnerable to||Poltergust 3000|
|First Appearance||Luigi's Mansion|
|Latest Appearance||Luigi's Mansion: Dark Moon|
|Relative(s)|| Boos - Minions
Luigi - Rival
Mario - Arch-Rival
King Boo is the main villain of the Luigi's Mansion series, he is a large Boo with a crown on top.
Before the events of Luigi's Mansion, Professor E. Gadd captured Boolossus. Using a device called a Ghost Portrificationizer, E. Gadd trapped Boolossus in a portrait and hung it in his Gallery inside his lab in Boo Woods. This angered King Boo, so he devised a plan to rescue Boolossus.
King Boo and his forces attacked the laboratory. The Boos reversed the settings of the Portificationizer and released Boolossus. King Boo then ordered that all the ghosts that E. Gadd had captured should be released as well. After releasing all the portrait ghosts, King Boo created a huge mansion and placed it next to the professor's lab. King Boo, his Boo minions, and the recently freed portrait ghosts decided to inhabit the mansion. With a huge mansion and an army of ghosts, King Boo decided to exact revenge upon Mario and Luigi by capturing them.
Hoping to recapture Luigi, King Boo sends him a letter. The message states that Luigi has won a mansion in a contest and provides the location of the prize. Luigi asks his brother Mario to investigate the mansion and says that he will arrive shortly thereafter. Mario and Toad travel to the mansion, but right after Mario enters, he is instantly overwhelmed by King Boo's forces and captured. King Boo then imprisons him in a portrait, similar to how Boolossus was imprisoned. Mario is placed in the Secret Altar in the basement of the mansion. With Mario captured, King Boo is ready to capture Luigi.
While waiting for Luigi, King Boo and his Boo minions wait behind a secret door in the floor of the Storage Room. When Luigi enters the room and reveals the secret door, the Boos spring out from the floor. However, the Boos (including King Boo) stop their surprise attack when they notice E. Gadd's Poltergust 3000 on Luigi's back. Luigi had been given the Poltergust 3000 so he could recapture the Portrait Ghosts. The Poltergust 3000 is one of the few things King Boo fears, and he and the other Boos scatter and hide in the mansion. King Boo travels to the Secret Altar in the mansion's basement.
The special key that Vincent Van Gore holds unlocks the path to the Secret Altar. However, he is locked in the Artist's Studio on the third floor of the mansion. After capturing him and retrieving the key, Luigi discovers that he still cannot enter the Secret Altar. If Luigi attempts to enter the Secret Altar without catching a certain number of Boos, King Boo blows Luigi to the Foyer, the entrance of the mansion. Since King Boo's power is related to the number of Boos in the mansion, Luigi can weaken him by capturing the Boos hidden in various rooms. After Luigi captures at least forty of the mansion's fifty Boos, King Boo loses his ability to blow Luigi from the Secret Altar. Once King Boo is weakened, Luigi enters King Boo's Secret Altar.
Upon entering the Altar, Luigi notices King Boo staring at Mario in the painting. King Boo turns around to face Luigi and states his desire to add a Luigi painting to the collection. After this, King Boo flies into the Mario painting hanging on the wall. The picture of Mario transforms into Bowser, then the new Bowser painting inhales Luigi into the canvas, transporting Luigi into an arena that resembles the mansion's roof. Luigi then confronts Bowser. In reality, this is a mechanical version of Bowser that King Boo pilots from the inside.
King Boo uses this Bowser disguise to attack Luigi, shooting flames at him, and even attempting to inhale him into its mouth. The decoy also has the ability to create three large spiked bombs and toss them at Luigi. Luigi can use his Poltergust 3000 to grab one of the spiked explosives and release it into the mechanical Bowser's mouth. This attack blasts the head off of the mechanical Bowser, causing King Boo to exit the machine and expose himself to the Poltergust 3000. Luigi begins to deplete the ghost's five hundred hit points. Meanwhile, the machine's head hovers around the arena, shooting icy blasts at Luigi. Eventually, King Boo flies back into the dormant Bowser body and the head reattaches itself, resuming the fight. Luigi repeats this process, slowly weakening King Boo, but after King Boo's life falls below two hundred HP, the head of the machine reattaches backwards whenever he returns to the Bowser body, causing the mechanical Bowser to run around aimlessly. Eventually, the mecha turns its head forwards and resumes the fight. Eventually, Luigi manages to completely drain King Boo's HP and capture him inside the Poltergust 3000
After the battle, Luigi receives King Boo's crown, worth 5000G (the value of only one Gold Coin) and adds it to his treasure collection. Upon returning to the mansion, Luigi quickly travels to Professor E. Gadd's lab. In the lab, Luigi connects the Poltergust to the professor's Portrificationizer, dumping its contents into the machine. Oddly, not only does the spirit of King Boo appears in the Portrificationizer, but also the Bowser mech. With King Boo captured, Professor E. Gadd hangs his new portrait in an empty room in his gallery.
King Boo will appear in the sequel. He has shattered the dark moon, causing the friendly ghosts of the mansion to go haywire and conform to his control.
Relations with the other charactersEdit
When Mario goes to Luigi's new mansion to investigate, he is captured by King Boo. Therefore, Luigi has to go rescue Mario by defeating the Boo leader. King Boo longs for Luigi in the painting too, for Luigi also has past dealings with King Boo.
King Boo and Mario have known each other for a long time. Also, King Boo imprisons Mario in a painting as a consequence for foiling his plans in the past.