Mel Brooks directed, as well as wrote, Young Frankenstein. He's got twelve directing credits as of press time, and Young Frankenstein earned him a best directing award from the Academy of Science Fiction, Fantasy & Horror Films, USA (source). Eat your hearts out, 1974 Oscar voters.
Brooks had cameo appearances in his three previous films—The Producers (1968), The Twelve Chairs (1970), and Blazing Saddles (1974), but Wilder didn't want Brooks on-screen in this one. Mel had a habit of breaking the fourth wall (i.e., addressing the audience directly), and Wilder was concerned it would distract viewers and destroy the fake-somber mood. So Brooks stays behind the camera in this one, contributing just his voice as a werewolf and a cat hit by a dart. (Source)