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. During his battle with Goku and Piccolo, Gohan seeing his father in danger explodes with rage and delivers a massive amount of damage to Raditz in a single blow. Taking advantage of the situation, Goku puts Raditz in a full nelson and demands Piccolo to kill them both with the Special Beam Cannon. Just before his death, he sneered that two more powerful Saiyans, Vegeta and Nappa, would be coming to Earth in one year's time. Source - Wikipedia