Robin Williams has signed on to play Theodore Roosevelt in the Ben Stiller starrer "Night at the Museum" for 20th Century Fox.

Helmed by Shawn Levy, the big-budget, live-action/CG comedy centers on a night watchman (Stiller) at a museum of natural history who discovers that its many exhibits awaken at night under the spell of a pharaoh's tablet. The exhibit of President Roosevelt, who founded the American Museum of Natural History in New York, is one of those that comes to life.

Carla Gugino, Kim Raver, Mickey Rooney, Dick Van Dyke and Bill Cobbs already have joined the cast.

Williams stars in Sony's upcoming family comedy "RV," directed by Barry Sonnenfeld, which opens April 28. His recent credits also include "The Night Listener," which was purchased by Miramax Films at the Sundance Film Festival. The Academy Award-winning actor is shooting Barry Levinson's "Man of the Year."

The film is scheduled to begin shooting next month in Vancouver and is slated for a holiday release.

He is repped by CAA, MBST Entertainment and attorney Gerald Margolis.