Nail is the personal guardian of Guru, the eldest Namek and father of all the Nameks. His role as personal guardian is very important because Guru is very ill. If Guru should die, the Dragon Balls will cease to exist on Namek.
Like all Nameks, Nail is aware of the severe consequences of allowing the Dragon Balls to fall into the wrong hands, and is willing to do whatever it takes to prevent this from happening. Nail is a very skilled fighter and later fuses with Piccolo.