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.

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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.