He was a disciple  of Tsurusennin, who is a rival of Kamesennin training to become an  assassin like Tao Paipai (Tsurusennin's brother). He first appeared  in the 22nd Budokai and presented himself to be quite an arrogant  character who was quite certain that he'll win the competition. All  that changed after he met Son Goku.

Son Goku defeated Tao Paipai. Tsurusennin wanted vengeance, even  if it means cheating in the competition and killing Goku. When  Tenshinhan faced Goku on the final match, Goku turned out to be such  a challenge that he no longer wanted to be a killer nor a disciple  of Tsurusennin. He only wanted to have a fair match against Goku  using his own strength. After defeating Goku by a very narrow  margin, he realized he did not want to learn the evil ways of  Tsurusennin and he along with Chao-zu became disciples of Kamesennin  instead. Thereafter, Goku became someone he constantly tried to  emulate. Even the presence of poweful Saiyajins does not stop him  from trying to become the best.