Majin Buu is the final and most powerful villian in DBZ. He is a demon created from majic by Bibi-Di. Buu was sealed away by Bibi-Di due to how uncontrollable he was. In the final chapter of DBZ babi-Di and Dabura gather enough energy to resurrect him. Buu was responsible for the deaths of almost every Earthling and destroys the Earth itself. During the Buu Saga he undergoes six transformations that occured for reasons such as absorbtion and removal of good and evil from within. Untrusting, the entire didn't donate their energy to Goku until Mr. Satan screamed for them to. With the energy Goku created a huge Genki Dama. With it Goku Finally killed Buu.