Robert Downey Jr. is set to star in his first big-budget action movie -- the comic book adaptation "Iron Man," according to a Dark Horizons website report.

Jon Favreau is directing the movie, which will be distributed by Paramount Pictures in May 2008, the site said.

Downey has the role of Tony Stark, a billionaire and genius inventor who is kidnapped and forced to build a highly dangerous weapon. Using his intelligence and ingenuity, Stark instead builds a high-tech suit of armor and escapes captivity. He uncovers a plot and must don his armor and protect the world, the site said.

Downey apparently won the role over Tom Cruise, who reportedly was also interested in starring in the film.

Principal photography on the project is set to begin in February.