Kid Buu

Kid Buu (魔人ブウ 純粋, Majin Bū Junsui; lit. "Majin Boo Pure"), also known as Majin Buu (魔人ブウ, Majin Bū), is the original and purest form of Buu. The first form he appeared in was actually the form that this Buu took after he had absorbed Southern Supreme Kai and Grand Supreme Kai millions of years earlier. Kid Buu appeared again, as the last form of Buu that appears in Dragon Ball Z, after all of the fighters he had absorbed were removed from his system (including Southern Supreme Kai and Grand Supreme Kai). Unlike his previous forms, this form of Buu's thought process is seen to be irrational and spontaneous, even destroying his own body to destroy the Earth.
Kid Buu is the final villain of the Dragon Ball manga. Although he appears smaller than any other form, he is more dangerous than any other forms of Buu, due to his full relentless evil and unpredictability. He is also completely free of restraint and has no trace of sanity and, because of this, is extremely volatile. He retains his childish personality, becoming amused and laughing hysterically at his own destruction of entire worlds.

Kid Buu's personality is very similiar to that of a very young child, in that he retains no form of compassion or remorse for any of his actions. Furthermore, due to his child-like personality and mind-set, he is incapable of developing empathy and comprehending the nature of his actions.
Buu's only reason for existence was to cause absolute destruction. He enjoyed the destruction he brought to the universe, revelling in the devastation he wreaks. He appears to enjoy testing the limits of his own power as well, seeking out Vegeta and Goku just to see how far they could push him. He is also utterly merciless, annihilating entire planets simply because Vegeta and Goku were not there. On the rare occasion he ever showed any restraint of his power, it was to make his "game" of destruction last longer instead of producing an instant kill. He is not a sadistic killer seeking to bring pain to his victims, as he seemingly does not care, or even know about pain, nor does he seek to conquer and rule over anything. He merely seeks to have fun the only way he knows how; creating havoc and destruction in the whole universe, similar to the Fat Version of Buu before Mr. Satan told him to stop killing. Only by Kid Buu gaining enlightenment through absorbing other beings is existence spared, and, by a Spirit Bomb fueled by every being on Earth and beyond.
Strangely, despite his destructive tendencies, Kid Buu seems to have a pure heart, as he is able to deflect Goku's Spirit Bomb back at Goku when it jams (King Kai earlier states that only someone with a pure heart could deflect the Spirit Bomb, though one being pure evil of heart may also be able to deflect it). His child-like personality is most likely what enables him to deflect the Spirit Bomb.
Though he is highly irrational and insane, Kid Buu does seem to have some reasoning abilities and intelligence, as he quickly realized that Goku refused to hit him with the Spirit Bomb as long as Vegeta was in the area and took advantage of it by pinning the latter to the ground.


Information from:
http://dragonball.wikia.com/
Information picture :
http://tekilazo.deviantart.com/