A person who's fooled into doing all the hard or dirty work for someone else is a stooge. If you're the butt of someone's mean jokes, you're also a stooge.
A slapstick comedian's sidekick — the one who gets a pie in his face or is hit in the head with a board — is a stooge. Now you know how the Three Stooges got their name! The word started out meaning "actor who assists a comedian," possibly derived from student, but it has evolved to be fairly derogatory. In crime, a stooge works for the mastermind: "She'll be arrested for selling the candy he stole, but she's just a stooge."