To steal the show is to unexpectedly become the star performer. A performer, be it an actor, a musician, a comedian, or a freak show geek, is said to "steal the show" if their performance is clearly the best one in the show, especially if it is better than that of the performers who got top billing.

For example, Pinky and the Brain stole the show from the Animaniacs (so much so that the WB had to spin off the former). In some concerts, sideman John Coltrane would steal the show from bandleader Miles Davis - not an easy task!