Saiyan Saga

Goku learns he is a Saiyan, and two stronger Saiyans are a year away.

The Saiyan Saga opens Dragon Ball Z: the first season of the anime contains the Raditz and Vegeta arcs. Five years after his victory at the 23rd World Martial Arts Tournament, Goku meets his evil older brother Raditz and learns that he comes from a race of extraterrestrials called Saiyans.

Lore & Background

After Raditz kidnaps Goku's son Gohan, Goku forms a truce with Piccolo; the battle ends with Goku restraining Raditz so that Piccolo can hit them both, mortally wounding them. Before he dies, Raditz reveals that two stronger Saiyans, Vegeta and Nappa, will come for the Dragon Balls in one year. Piccolo takes Gohan into the wild to train for the coming battle, while Goku trains with King Kai in the Other World. When the Saiyans arrive, Vegeta fights Goku and is severely beaten by Goku's Kaio-ken technique; he resorts to his Great Ape form but cannot beat the rest of the heroes because of the injuries dealt by Goku, Gohan, Krillin and Yajirobe.