Justin Theroux to write Iron Man II
Robert Downey Jr starred as the eponymous hero in the hit movie, which raked in $101 million in its first three days of release.
Theroux is relatively new on the scene, having recently completed his first screenplay for forthcoming movie Tropic Thunder.
However, he already has several acting credits under his belt, including roles in Mulholland Drive, Charlie's Angels: Full Throttle and television series Six Feet Under.
Variety reports that the 36-year-old is on board to pen Iron Man II, with Downey Jr and director Jon Favreau both set to return.
The movie will continue the story of Downey's character Tony Stark - an arrogant industrialist who becomes a superhero after inventing an armoured suit.
Marvel Studios was quick to give the sequel a green light, after the original movie grossed $570 million (£280 million) worldwide.
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