Waluigi - Mario Series
Waluigi is the absolute definition of a sidekick. He was literally created for Wario to have a doubles partner when playing tennis against Mario and Luigi. As such, Waluigi doesn't do much on his own, and you almost never see him without Wario. Waluigi is a tall,lanky, goofy sidekick that seems to just always screw things up. The pair don't exactly create a dynamic duo.