Mr. Buu (Good Buu)

Once Majin Buu expels Evil Buu, he becomes pure good, but loses most of his power. The fat Majin Buu, who is now named Good Buu (魔人ブウ：善), has a brief fight with Evil Buu in which he is greatly outclassed and ultimately absorbed through ingestion, allowing Evil Buu to become Super Buu. Though this is the weakest Buu, his power is still immense compared to most other characters in the series. Once he is absorbed, all of the Kai's influence goes into his being, allowing Super Buu to be uninhibited by any form of good, with the exception of Good Buu's memories of Mr. Satan and Bee, which stops Super Buu from attacking them on multiple occasions.
After re-fusing into Super Buu, Good Buu basically represents all the power gained by Kid Buu through the absorption of the Supreme Kais. Once this power is removed from Super Buu, he transforms back into Kid Buu. Later, after Kid Buu is defeated, Good Buu is called Mr. Buu by the main cast (excepting one notable instance in the Neko Majin manga, where he still refers to himself as "Majin Buu" while he was on a walk from Satan City); although Mr. Buu is the same as the fat Buu on the outside, he is noticeably different on the inside. He no longer widens his eyes in fits of anger. All the evil tendencies seen in the fat Majin Buu are gone and he is now pure good.


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