Majin Buu is without a doubt the most powerful villain faced by the Z Fighters during this anime and his story is told at the end of the Dragon Ball Z anime over the course of the Majin Buu Saga.
Majin Buu was created thousands of years ago by the evil wizard Bibidi. Following Bibidi's orders Majin Buu destroyed countless worlds and murdered billions but as time went by Majin Buu became more and more difficult for Bibidi to control. Because of this Bibidi began to seal Buu up in a magic ball as they moved between worlds. Once they arrived Bibidi would cast a spell that would unleash Buu upon the planet, and when Buu was finished another spell would lock him up again. Buu was only stopped from destroying the Earth because Supreme Kai confronted and defeated Bibidi before he could release Buu. With nobody to cast the spell to unlock the ball Buu was sealed forever. The Supreme Kai considered attempting to destroy Buu while he was in the ball, but considered it too risky as there was a good chance all he would achieve would be to release Buu.
But Bibidi had a son, the evil wizard Babidi who knew all of his father's spells except the spell to release Buu. But through clever scheming Babidi was able to release his father's creation.
The First Buu we see is 'Fat Buu'. Fat Buu deserves his name, being wider than he is tall. He is bright pink in colour and his body seems to have the consistency of chewing gum. He wears billowy white trousers held up with a black belt with a gold buckle bearing the 'M' majin symbol. He wears bright yellow boots and bright yellow gloves. He also wears an black jacket and a purple cape. He is constantly grinning, his eyes seem shut all the time and his head has a small tentacle attached to it. Initially the most surprising thing about Buu is his childlike manner. This villain is unlike his predecessors Frieza and Cell who were ruthless killers. This creature dances around the place, making unfunny jokes which only he finds amusing and he speaks in a high-pitched voice. Many of the Z-fighters underestimate Buu because of his actions. The evil Dabura makes this mistake and attacks Buu and in this conflict we begin to understand the creature's powers. Buu has amazing regenerative capabilities. Any damage done to his body can be almost instantly repaired. When a hole is blown in Buu's stomach it is repaired quickly and it seems nothing ever happened to him. Dabura is dispatched quickly with Buu's favourite technique, a beam of pink energy that shoots out of his head tentacle. This beam has the ability to convert anything it touches into anything Buu wants, usually food. Dabura is turned into a cookie and gobbled up. Buu goes up against Vegeta next and he manages to trounce his opponent. Vegeta comes to the conclusion that he must do everything he can to safeguard his family and adoptive home, so he suicides in a massive blast that blows Buu to pieces. Despite his sacrifice it isn't enough and Buu simply reforms. Buu is then directed by Babidi, who threatens to return Buu to his ball unless Buu complies with Babidi's orders. Babidi is on a mission to find Piccolo, Goten and Trunks because of their interference earlier. To help speed this process up he telepathically communicated with the people of Earth, forcing them to watch Majin Buu as he attacks a city. Buu converts the entire population into jawbreakers which he sucks up in one mighty gasp and eats. He then levels the city much to Babidi's delight. The next city suffers the same fate, as he turns the population into chocolate bars. Eventually Fat Buu grows tired of Babidi and through simple trickery is able to dispose of the wizard by punching his head off. In between bouts of mass destruction Fat Buu builds a house (naturally from cement made from people) and this is where he meets Hercule. Hercule lied about destroying Cell several years ago so now that the Earth is in danger again the people have turned to him for help. Arriving at Buu's house though Hercule befriends the pink monster and even convinces him to give up killing. Buu adopts a puppy called 'Bee' and things seem to be going well. But two men arrive on the scene and shoot the puppy and then Hercule. While Buu heals both the strain of keeping his promise and his desire for revenge cause Majin Buu to split into two people, Good Buu and Evil Buu.
The second Buu we see is Evil Buu, who looks like a grey and desiccated version of 'Fat Buu' at first. Evil Buu kills the two men who shot Hercule and the puppy and then confronts and fights the Good Buu. Good Buu attempts his conversion attack on Evil Buu, but Evil Buu simply reflects it back at him. Good Buu is turned into chocolate and is eaten by Evil Buu who then changes. Evil Buu is now muscular, wearing just the billowing white pants and black boots. He is also considerably more powerful. With the ability to sense life energy now, he journeys to Kami's lookout where the Z-Fighters and their loved ones are waiting for Goten and Trunks to master the fusion technique so that they could fight Buu. But Buu is a day early and the boys aren't ready. In an act of desperation Piccolo pleads with Buu to return to the surface and wait an extra day, saying their are plenty of people for Buu to have fun with. Piccolo knows that Buu's victims can be ressurected with the Dragonballs. In response Majin Buu launches his 'Human Extinction Attack', an assault that kills every Human on Earth with the exception of Tien, Chaotzu, and Hercule. Buu agrees to wait one more hour before facing Goten and Trunks. In that period Goku's wife Chi-Chi slaps Buu and verbally remonstrates him for killing her son Gohan. Buu's response is turn Chi-Chi into an egg which he proceeds to crush. Buu fights Gotenks in the Hyperbolic Time Chamber but when it appears Gotenks is losing Piccolo destroys the entrance trapping them inside forever. Buu is shocked to learn he will never again have chocolate and in his rage he punches a hole between dimensions. Returning to the lookout he turns everyone can find into chocolate and devours them. Gotenks and Piccolo copy buu and escape but too late to help their friends and family. Buu fights Gohan next, but Gohan who has been training in the otherworld proves too much. Buu therefore deploys yet another of his techniques, the ability to absorb other fighters. He uses this against Piccolo and Gotenks to become Super Buu.
Super Buu is the most intelligent form of Majin Buu. He has the face of Piccolo and the powers of Piccolo and Gotenks added on to his own. His head tentacle is now huge, stretching down past his waist. His assault on Gohan is devestating and it compels Goku to return from Otherworld with a plan to fuse with his son and defeat Buu. But Goku's plan goes awry when Buu absrobs Gohan. Luckily Vegeta arrives from Otherwold with special dispensation to fight Buu. Goku and Vegeta fuse to form Vegeto and they proceed to fight Majin Buu. Buu has difficulty against the fused being but eventually manages to turn them into a coffee flavoured piece of chocolate. But this piece of chocolate still possessess intelligence and all Vegitto's powers. Unable to hit the chocolate Buu is compelled to restore Vegitto. But he then manages to absorb them. Delighted with his seeming victory Buu goes on a rampage, noting only that he wished he'd kept some Humans around to make it more fun. As he is about to destroy the Earth however his power vanishes and he reverts to his Evil Buu form. Vegeto had intentionally been absorbed so they could free the others, but Buu's digestive system had unexpectedly separated Vegitto back into Goku and Vegeta. Having found their sons and Piccolo encased in pods in the monster's head they detached them. Buu then entered his own head and fought them, their conflict only coming to a close when Vegeta detaches the pod of the Good Buu. This causes Majin Buu to mutate into his first and last form.
Kid Buu is the final form of Majin Buu. He cannot be negotiated with. He has no remorse. He has no mercy. His sole reason for existence is to kill and to destory. And he enjoys it. This version resembles nothing less than a small Evil Buu. But he is far more powerful. Supreme Kai reveals that this is the original state of Majin Buu. Thousands of years ago Buu was confronted by the Five Kais. North Kai and West Kai were both killed by Buu whereas South Kai and Dakaiyo were absorbed. It was the absorption of Dakaiyo that turned Buu into the childish Fat Buu we initially see. South Kai and Dakaiyo however actually weakened Majin Buu because of their good influence. Now that they are gone and the original Buu is back he is a creature of pure Evil. His first target is the Earth which in a psychotic episode typical of him he blows up the minute his transformation is complete. Vegeta, Goku, Hercule, Dende and the puppy Bee are the only survivors. Kid Buu tracks them to the otherworld and engages in one last climactic battle with Goku and Vegeta. But Goku and Vegeta aren't strong enough. Hercule steps in and challenges Buu, but Buu finds himself unable to attack. Eventually he spits out something that turns into Good Buu. Hercule overcomes his cowardice to fight for his unconcious friend. When Good Buu wakes up he saves Hercule and then starts fighting Kid Buu. While this is going on Vegeta hits upon a plan. He has Dende, Supreme Kai and Elder Kai travel to New Namek where they summon Porunga, the Namekian dragon. Vegeta has them wish for the restoration of Earth and the resurrection of everyone killed since the morning of the World Martial Arts Tournament, except for the most evil. The Dragon complies. Goku is amused to find Vegeta is ressurected, pointing out this means his is no longer evil. Vegeta then explains his plan, a Spirit Bomb, made from the freely given energy of the people of Earth. He communicates to the entire planet via King Kai but only their friends and family believe him, the rest thinking it was all a dream. With the Good Buu now pounded into the dust Vegeta has to hold Kid Buu off so that the Spirit Bomb can be completed. Goku asks the people of Earth to help but only a few people Goku helped in the past give up their energy. As Hercule hears this he gets more and more angry until he starts shouting at the people of Earth who hear him. Hercule realises this and then proceeds to exhort them to give up their energy so that he can defeat Buu. He knows this is a lie and explains to Goku he doesn't believe they'd do it for anyone else. Thanks to Hercule the Spirit Bomb is finished but Kid Buu has defeated Vegeta who is now too weak to move. Kid Buu knows Goku wont fire the Spirit Bomb because it would destroy his friend and so he stands on top of him while he continues to blast Goku. Out of nowhere comes the Good Buu who uses the last of his strength to knock Kid Buu over and pin him. He tells Hercule to grab Vegeta. Kid Buu quickly recovers though and blasts the Good Buu but the way is now clear for Goku who fires the Spirit Bomb. But Goku is exhausted and Kid Buu is not only able to stop the Spirit Bomb, he is able to take control and fire it back at Goku. All seems lost until Vegeta asks Dende to make one last wish, to restore Goku's strength. With Goku renewed, he takes back control of the Spirit Bomb and directs it back at Buu. Buu tries to block it but it begins forcing him backward. For the first time his expression is one of fear, something he brought to so many.
Goku says 'It looks like this is the end of the road Buu. It's a darn shame. When I first met you, you were like a naughty little child who didn't know any better. But the battle between good and evil that was taking place inside you took place on the outside, and the darkness overpowered the light. From then on you changed. You were ruthless. You were a living nightmare and you enjoyed every minute of it.And that's why it has to be this way. You've got to learn what it feels like to have your life taken away against your will. It's wrong. Maybe you'll come back one day as a better person i hope. We'll have ourselves a little one on one. I'd like that.'
Goku then salutes his terrified adversary. 'Adios. See you on the flipside Majin Buu'
With that he triggers the Spirit Bomb. Majin Buu is engulfed. His expression is a mixture of overwhelming terror and agony. With one drawn out scream his body disintegrates and he is gone. This was the end of Majin Buu, the villain who caused more death and destruction than any other opponent the Z fighters faced. Goku later wishes on the Dragonballs for the people to forget about Majin Buu to allow the Good Buu to walk around without being feared. And ten years later at the World Martial Arts Tournament the Z fighters meet a boy called Uubu. This boy is the reincarnation of Majin Buu. Goku agrees to train him, and they fly away. This also marked the end of Dragon Ball Z