Dragon Ball Z Season 1 Episode 20

Goku’s Ancestors

Goku's next task in King Kai's training is to hit the grasshopper, Gregory, with a heavy mallet. After a long chase, it seems that Goku can't hit Gregory yet. While taking a break, King Kai tells Goku about the Saiyan people. They were a warrior race who shared a planet with the smarter, though weaker, Tuffles. Eventually, the Saiyans overpowered the Tuffles and stole their technology. Willing to stop the Saiyans from destroying Earth, Goku continues his training and manages to hit Gregory. Now King Kai will train Goku himself in the ways of the Kaio-Ken.