The famous acting teacher Konstantin Stanislavski coined a famous expression: “There are no small parts, only small actors.” What he meant was that any part can make an impact, provided it's executed by an actor with creativity, skill, passion, or bravery. If a part doesn't register, it's simply because the actor wasn't trying hard enough or didn't fully commit.
That's an important thing for actors to understand, because even a small supporting role has the ability to launch someone's career. The following stars all had that happen. They're some of the biggest names around, and in every case, they parlayed a minor or secondary part into a one-way ticket to the A-list. Some of them matched - or, in a couple cases, even upstaged - more established stars. Even though they weren't the headliner, these performers gave 100% to their characters, delivering performances that made audiences sit up, take notice, and say, “Who is that?”