Robert D. Siegel is an American screenwriter known for The Onion Movie and The Wrestler, as well as the writer and director of Big Fan. His movie The Wrestler won the Golden Lion at the 2008 Venice Film Festival and has earned several Best Picture nominations. Big Fan premiered at the Sundance Film Festival in 2009. It was revealed in an online interview that Siegel attempted to write drafts for a comedy film but it ended up being a drama because of the conflicts in the film as well as avoiding Patton Oswalt being typecast as a comedic character.

Siegel is a graduate of the University of Michigan who later became senior editor of The Onion from 1996 to 1999, and editor-in-chief from 1999 to 2003.