Jack Black has signed on to star in the Ben Stiller-directed comedy Tropic Thunder, with Robert Downey Jr. and Jay Baruchel, according to Production Weekly.

In the film, everything goes wrong during the making of a big-budget war movie, and the actors end up becoming the commandos they are playing. Stiller, Justin Theroux and Etan Cohen wrote the screenplay.

Black will play Jeff "Fats" Portnoy, an overweight gross-out comedian, who's forced to kick his drug addiction while filming on location in the jungle. Downey will play Kirk Lazarus, the greatest actor of his generation and a four-time Oscar winner. Baruchel will play Kevin Sandusky, an unknown actor on the set and Stiller plays Speedman.

Shooting is set to begin in July.

Tropic Thunder was released August 13th, 2008 and stars Jeff Kahn, Robert Downey Jr., Anthony Ruivivar, Jack Black, Jay Baruchel, Brandon T. Jackson, Ben Stiller, Eric Winzenried. The film is directed by Ben Stiller.