Piccolo is from the planet Namek. He first appeared in the DB series. He was an evil offspring of the Great Elder. He was evil and hated everyone. He was one of the arch enimies of Goku.
In the DBZ series he was forced to join Goku and fight Raditz. He later trained Gohan to help out in the battle against the saiyons. He forms a bond with Gohan and shows friendship toward him He even takes his own life to save Gohan from Nappa by stepping in front of Nappas attack.
Later in the DBZ series he becomes good friends with the Z Warriors especially Gohan and Goku. He later on trains Goten Gokus second son.