Raditz is the biological brother of Son Goku and the eldest son of Burdock. Raditz went to Earth to help in the planet's invasion, and to persuade his younger brother Goku to join the Saiyans in their conquest. However, disappointed to discover that Goku had lost his memories and adjusted to life on Earth, Raditz kidnapped Gohan and tried to force Goku to become an ally.


(Source: Wikipedia)