Nappa is an Elite Saiyan Warrior from the Planet Vegeta. He has appeared in the " Budokai" games and the " Budokai Tenkaichi" games but not in either of the " Shin Budokai" games. He is also in the newer " Burst Limit" game and some games on older platforms such as the SNES.
He comes to earth with Vegeta, searching for the Dragon Balls, so that they can wish for immortality. When they arrive, he destroys an entire town as a greeting, and proceeds to destroy a large amount of the military and navy for fun. He has the typical Saiyan aggressiveness and love of destruction and fighting.
In the battle with the Z fighters, who were protecting the Earth, he showed the overwhelming power of an Elite Saiyan Warrior, that easily defeated Tien, Chiaotzu, and Piccolo. He also showed the Z fighters that Elite Saiyans, like himself and Vegeta, are not susceptible to a certain weaknesses common to Lower Class Warriors like being defenseless when their tail is grabbed.
He was then executed by Vegeta after being easily defeated by Goku who had been wished back to life with the Dragon Balls after receiving training from King Kai in the afterlife. Vegeta deemed Nappa as weak because Goku was a lower class warrior who should have hardly been able to touch him.
In the Dragon Ball GT anime, he escapes from Hell and goes on a rampage on Earth. Vegeta finds him and after a short exchanging of words, Nappa is killed again instantly.
Nappa is a very large man with big muscles. While he was much stronger than most of the Z fighters who were smaller than him, it is proven that size really doesn't matter when Goku easily defeats him.
He wears Saiyan Armor with a gold/yellow and dark blue colour scheme, and like Vegeta at the time, has his tail wrapped around his middle to keep it out of the way. Nappa also has a thin mustache, he is one of the few Saiyans seen with facial hair, the other notable person being King Vegeta. Vegeta also had a mustache at the begining of Dragon Ball GT. Nappa wears a blue scouter to determine the power levels of his various opponents. Nappa usually has a very angry or mischievous look on his face, and very serious looking eyes.
While he had no hair when he invaded the Earth with Vegeta, he is shown in the Bardock special to have had a small amount (at least by Saiyan standards) of black hair on the top of his head. It is not known if he either shaved his head or if like humans, some Saiyans possibly lose their hair as they get older.