Majin Buu Character Facts

Although he is one of the most powerful entities in Dragon Ball Z, Majin Buu is often playful and displays his childish personality, revealing he destroys things for fun simply from old instructions from his master, stopping once told what he was doing was wrong thanks to the Grand Supreme Kai's personality showing in him. Though he is playful and silly, his evil side is readily apparent, especially shown when his eyes widen, and steam shoots out of the holes on his body. His extreme anger issues show themselves often, when he is even slightly made fun of, or starts to lose in a battle. He finds enjoyment in taking the lives of many and shows no remorse, though this is because he treats everything as a game. In battle, he fights in a bullying manner, using his immense size to outflank his opponent. During his second battle against Gotenks, Gotenks was preparing the Super Ghosts of his Super Ghost Kamikaze Attack for battle. Piccolo showed Gotenks that Buu had already regenerated from the last Super Ghost attack. Super Buu was also lying on his stomach, drinking a soda (though it looked like a milkshake) and reading a magazine, much to Gotenks' fury and embarrassment. Also, when Vegeta and Goku were preparing for battle, Kid Buu was sleeping, much to Goku's surprise. 
Despite the pleasure he takes in mass-murder, it is later revealed that he only committed such acts because he was unaware of their immorality, and because he had been commanded to do so by Babidi, and Bibidi before him. The Grand Supreme Kai's presence is more influential in this form than in Super Buu, who is mostly evil and is influenced very little by the Kai. He literally struggles with the evil inside himself, with the evil winning and usurping near complete control, Majin Buu becoming far more dangerous as a result. 
Buu also possesses an enormous appetite for sweets, shown to far exceed even Goku's eating habits, as Buu was still hungry after he once turned a whole city of people into candy and ate them. Majin Buu only has to sleep for about five seconds to get the results humans get from hours of slumber. He is extremely naive, as he was completely ignorant of Mr. Satan's (inept) attempts to kill him. 
The fat version of Majin Buu is the result of Ultra Buu's absorption of Grand Supreme Kai, the supreme ruler of all Kais. The merging of the juvenile and immature Kid Buu with the benevolent and innocent Grand Supreme Kai resulted in a child-like carefree being who, despite his behavior, possesses power that far surpasses that of a Super Saiyan 2. Of note, absorbing Grand Supreme Kai granted Majin Buu the ability to speak fluently, although he usually refers to himself in the third person. Buu became calmer and easier to control after absorbing the Grand Supreme Kai,[9] and Bibidi then decided to seal him in a Sealed Ball.