He was Goku's best friend, and useful ally for most of both series.
I still remember when he was almost sort of evil when he first trained under Master Roshi.
But it didn't take long for him and Goku to become friends than rivals.
Then he dies.
Well good thing people can be wished back in the land of Dragon Ball.
He managed to be decently okay during Dragon Ball Z.
He was strong until the juggernauts hit the scene.
But he did play a vital role in Vegeta's defeat.
And he did help Gohan a lot on Namek.
How he managed not to die during the fight with the Ginyu force I'll never know.
He couldn't do much against Cell.
After this point in fights, Krillin was about as useful as a foam sword.
He then just plays the role of slightly creepy lonely guy.
Got to give him props for getting a robot pregnant.