Buu is a fictional character in the manga Dragon Ball/Dragon Ball Z and the anime Dragon Ball Z and Dragon Ball GT.

Buu is the most powerful enemy faced by the Z Fighters in the series. While incredibly powerful himself, Buu gets a great deal of his strength by absorbing others, adding his victims' power to his own and he has also killed nearly every character. He absorbs by either turning the victim into food and eating them, or covering the victim with his slime and consuming them.

Buu was created by the evil wizard Bibidi many centuries ago and was used to destroy worlds.

Buu then attacked the Kaioshin, the gods of the universe. He killed North Kaioshin and West Kaioshin, then proceeded to absorb South Kaioshin, becoming the hulking Huge Buu. After nearly killing East Kaioshin, he then absorbed Dai Kaioshin and became Majin Buu, a fat Buu who was kinder and weaker due to Dai Kaioshin's good nature.

As he became more and more difficult to control, Bibidi took to locking him inside a ball while traveling. While Bibidi was on his way to Earth, and Buu was locked in his ball, East Kaioshin attacked and killed Bibidi.

Bibidi had a son though, Babidi, and he figured out how to release Buu. Once released, Buu hardly seemed like a terrible villain, more like a naughty child. His power was not to be underestimated though, as he seemed impervious to assault and could turn even powerful warriors like Dabura into a harmless (and easily consumed) piece of food (which is probably a form of absorbing). Even Vegeta's devastating suicide attack on Buu only momentarily harmed him. He was split into hundreds of minuature Buu's, which then recombimed to become Buu again.

Buu eventually became sick of Babidi's bossing him around and destroyed him. He then makes friends with Mr. Satan (Hercule), who makes him promise to stop killing, and even adopts a puppy. All seems well until two thugs shoot Hercule and the puppy. Buu, torn between his desire for revenge and his promise, becomes frustrated to the point that he releases steam from his head which condenses into another Buu. The new Buu, Evil Buu, is thin, grey and has taken the bulk of Majin Buu's power. He is a stark contrast to the now good Mr. Buu, who looks the same as Majin Buu.

The two Buu's battle each other until Good Buu unleashes his conversion beam on Evil Buu. Being more powerful, Evil Buu simply reflects it right back. Good Buu is turned into a piece of chocolate and eaten by Evil Buu, resulting in Super Buu, a muscular being who has a green tongue, and an annoying habit of cracking his neck.

Super Buu then goes through several stages of increasing power. He first absorbs Piccolo, then Gotenks and finally Son Gohan. At this point he's at his peak of power, and nearly unstoppable. Vegeto managed to get inside of Buu and removed all of his absorbed victims (South Kaioshin and Dai Kaioshin are presumed to be part of Buu, so they aren't released).

This caused Buu to revert to his original form, Kid Buu, an unrepentant sociopath who lived to destroy and could not be reasoned with. Buu made a huge energy ball and destroyed Earth and only Goku, Vegeta, Dende, Hercule and Bee escaped with Kibtokai's help. Buu later appeared on the kai planet and fought Goku and Vegeta. Mr. Buu appeared again during the Kid Buu and Son Goku fight, being spat out before Kid Buu attacked Hercule. Mr. Buu was able to distract Kid Buu for a considerable time, helping Goku gather energy for his Super Genki Dama from the Earth. Hercule later convinced the people of Earth to give him the energy needed. After the defeat of Kid Buu, Mr. Buu was able to lead a "normal" life with Hercule and Bee.

In Dragon Ball GT, Mr. Buu fused with Uubu.