Kid Buu

Pure Majin Boo or Kid Buu (Funimation dub) is the original form of Majin Boo, controlled by the wizard Bibidi, who has existed since time immemorial and is also the final antagonist in Dragon Ball Z. He transformed from into Super Buu when Vegeta tore down Majin Buu from his head. The original Majin Buu had his appearance before absorbing South Kai and Grand Supreme Kai, and he is a mindless killing machine. With the purity and rationality of the Grand Supreme Kai's influence inside of him gone, he is more dangerous than ever. As he is now pure, unrestrained rage and evil.

History
After Super Buu becomes Kid Buu, his first act was to blow up the Earth with a giant pink energy ball after Vegeta tells him if he wants to destroy Earth, he has to fight them first, killing Gohan, Goten, Trunks, Piccolo, Tenshinhan, Chiaotzu, Krillin, Yajirobe, and (though it is also possible that Super Buu killed him with his Human Extinction Attack first, depending on whether or not he evaded it) Android 18, Marron, and everybody else on earth.

He then used Instant Transmission to destroy planets until he arrived at Grand Supreme Kai's planet. He fought Krillin and Yamcha, who were already dead, and nearly blew up the planet before Full power Super Saiyans Goku and Vegeta powered up to draw him over to Kai's planet.

Through rock-paper-scissors, they decided Goku should fight him. Goku first fought Kid Buu in his Super Saiyan 2 state and later, as a Super Saiyan 3, evenly matching with Pure Boo, but began losing his energy due to not having mastered the Super Saiyan 3 state and his earlier battles against Boo, Vegeta fought Kid Buu as a distraction and powered up to a Super Saiyan 2, even though he knew that if he died while already dead, he would not exist anymore and could never be revived again. Vegeta was at a disadvantage and Buu was about to end his existence when Mr. Satan, believing himself to be in a dream, appeared and insulted Buu. Buu tried to attack him, but was unable to because he was getting a headache caused by the original Majin Buu, whom Pure Buu spit out like a piece of chewing gum.

Kid Buu then fought Good Buu, but Kid Buu had all of the advantage and brutally beats him with Mr. Satan attacking him (and not doing any damage). When Goku lost all his Super Saiyan 3 energy, Vegeta devised a plan that involved using the Dragon Balls to revive Earth and all its inhabitants who has died since the 25th World Martial Arts Tournament except for the evil ones (Vegeta and Old Kai returned as well). Goku then began gathering energy for a Super Spirit Bomb but no one on Earth (aside from other Z Warriors and their friends and families) would give up energy. When Majin Buu was clearly losing energy and close to death, Vegeta re-entered the battle, and Goku asked people to give up energy. A few of them did, but everyone else thought he was trying to steal their souls - until Mr. Satan asked them to, and they did, believing that Satan was the one fighting Buu.