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 East Kaiôshin (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.
Bibidi had a son, the evil wizard Babidi who knew all of his father's spells except the spell that could release Buu. But many years after Buu's containment, Babidi through clever scheming was able to release his father's creation (Babidi Saga).
Outline
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 a 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.
When Buu comes out of the egg, Goku and Vegeta sense his energy and put the battle on hold. The realize the true danger and go to fight him, but Vegeta tricks Goku into letting down his guard and attacks him from the back. He then takes a Senzu bean and flies off to fight Majin Buu.
Initially the most surprising thing about Buu is his childlike manner. This villain is unlike his predecessors Frieza and Cell who were ruthless killers that seemed to only care about pain and suffering to others. This creature dances around the place, making unfunny jokes which only he finds amusing and 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. Much faster than Cell's and 10x faster than Piccolo's. 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. Kind of a childish attack, but it got the job done.
Vegeta finally makes his way to the location of Buu and Babidi's ship. His entrance does not go unnoticed. He completely destroys Babidi's ship. Buu goes up against Vegeta 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. Realizing that Trunks was nearby, he hugged his son for a final goodbye and so, he suicides in a massive blast that blows Buu to pieces. Despite his sacrifice it isn't enough and Buu simply reforms.
Bulma and the other supporting characters go around collecting the Dragon Balls. They summon Shenron, and make the first wish that everyone who died since the morning of the World Martial Arts Tournament comes back to life. All the people killed by Majin Vegeta, and also Kibito come back to life. but Goku teleports there, and stops them from making the next wish, and Shenron goes away for 6 months instead of a whole year. He teleports them all to Kami's lookout.
Kai has wandered around trying to find Gohan, and the wished-back Kibito finds them both and heals them. Kai then teleports them all to his own planet. The first mortal to actually step foot on the Kai plane. Gohan meets the Elder Kai and this is where Gohan begins training with the Z-Sword.
Goku now begins to teach the boys Goten and Trunks how to do the Fusion Dance. Goku learned this technique from the Metamori, during the seven years after Cell's defeat in the Other World. They will take a long time to learn this, more time than Goku has. Since Goku is pressed for time, he ends up showing Piccolo the dance for when Goku leaves. Meanwhile, 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 Babidi 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.
In order to buy time for Trunks to get the Dragon radar, Goku approaches Fat Buu and Babidi, and starts giving them a show of his strength. He figured this would be enough to impress Babidi and stall him, and give Buu something to do to stall him. Goku transforms into a Super Saiyan, very easily, and then a Super Saiyan 2, and finally after a drawn out show, transforms into the long haired Super Saiyan 3. Babidi didn't seem too impressed with the first two forms since he saw them in Vegeta and Gohan, but the third one was different. This still didn't give Goten and Trunks enough time, so Goku decides to battle against Fat Buu. The battle starts off quick paced, where many people around the Earth can feel the energy flow. Goku once again holds back his efforts, because he knows that it isn't his job to save the Earth anymore. After awhile, Goku loses the upper hand in the battle to Buu and Goku decides to High Tail it out of there. That bought Goku the time he needed, and then he takes off.
Fat Buu grew 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 and his childish like acts, Fat Buu builds a house (naturally from cement made from human bodies) and this is where he meets Hercule (Mr. Satan).
The Super Saiyan 3 transformation has decreased Goku's time left, and when he arrived at the lookout, it was too late. So he has to go back to the Other World. Piccolo continues teaching the boys the fusion, after one mishap where they failed miserably, they successfully fuse, and fly off to fight Buu, but he pummels them.
In Other World, Goku finds Gohan alive, and while training the Z-Sword breaks. Out comes Rou Dai Kaioshin (Old Kai) who begins to unlock Gohan's inner powers. Called the "Mystic" powers.
Mr. Satan 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, Mr. Satan 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 Mr. Satan. 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. Evil Buu proves too much for Good Buu and eventually onsorbs him. Creating a whole new, more powerful Buu.Continues ... Fusion Saga.