Fellow warrior and Saiyan with Vegeta, Nappa comes to Earth with Vegeta to destroy it. This muscular Saiyan does much of the early fighting on Earth including eliminating directly or indirectly through the Saibaimen. He planted seeds which turn into the six Saibaimen and battled the allies.
Nappa may have more brawn than brain and gets over excited and careless when fighting. Vegeta coaches him to calm down and states that he can win the fight. It is during his Kamehameha beam attack on Gohan and Krillin that Goku swoops in with his KAIO-KEN attack to thwart Nappa. Nappa is inferior to and afraid of Vegeta --and for a good reason. When Nappa loses the fight to Goku, Vegeta turns on him and immediately eliminates him for his weakness.