Majin Buu is the beast Babidi revives. He's a kind being (Sorta) and childish. He fought Majin Vegeta and SSJ3 Goku. Buu later meets Hercule who stays with him. In the battle with Kid Buu, Majin Buu helps out. In GT, Buu fuses with Uub to make Majuub. Majin Buu is playful and childish because when Kid Buu absorbed Grand Supreme Kai, Kid Buu transformed into Majin Buu.