Goku is the hero of the series, he is a saiyan sent to earth when he was an infant to
destroy earth for conquest, but when his pod lands he gets amnesia and is found by a
martial arts master. Goku becomes pure of heart and willing to help anyone and even as
a boy it is obvous that he is the most powerful fighter in the world. After defeating
Raditz and Vegeta, Goku goes to planet Namek to help defeat Frieza where Goku is the first saiyan to turn Super Saiyen in a millenium. By the end of Dragonball Z, Goku has attained Super Saiyan level 3,and by the end of Dragonball GT he and Vegeta have attained Super Saiyan level 4.