Nappa is an elite Saiyan warrior that accompanied Vegeta to Earth in search of the Dragon Balls. He has been Vegeta's attendant ever since Vegeta's childhood, and has a somewhat violent nature, even among Saiyans. He survived the attacks of Tenshinhan and Chaozu which drained their lives and put Piccolo to death with his incredible might, but fell powerless to Son Goku who had returned to Earth with new training from North Kaio. Vegeta ordered him to stop fighting Goku due to Goku's clear dominance over him; He was then executed by Vegeta when Goku defeated Nappa.

(Source: Wikipedia)