Robert D. Siegel is an American screenwriter who made his movie debut as a writer in 2008 with the comedy The Onion Movie. Following his debut, he directed his first movie in 2009 titled Big Fan, starring Patton Oswalt, Kevin Corrigan, Marcia Jean Kurtz, Michael Rapaport, and Scott Ferrall. The movie screened at the Sundance Film Festival and was well-received by the audience. Siegel has worked on other movies such as Turbo, Cruise, and The Founder.