Ubb is the reincarnated, human form of Buu. Uub's qualities are the opposite of everything that Kid Buu was. Uub is kind and friendly. At the end of Dragonball Z, Goku leaves his friends and family behind to train Uub. 10 years later at the beginning of Dragonball GT, we see Goku and Uub just finishing up their training on Kami's lookout. Later in the series he gets to put his power to the test against the terrible Baby, eventually joining with Majin Buu to realize more power that he could ever imagine. He is then known as Majuub.