Robert Downey Jr. and Jay Baruchel have signed on to star in the Ben Stiller-helmed comedy "Tropic Thunder" for DreamWorks Pictures and Red Hour Films says The Hollywood Reporter.

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. 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. Stiller, Justin Theroux and Etan Cohen penned the screenplay.

Shooting is set to start in July.