The trailer for Robert Downey Jr's new comedy has been released amid controversy over the actor's casting as black man.

In the promotional clip, the actor is virtually unrecognizable after donning make-up and afro hair and brown skin for his new film Tropic Thunder.

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Controversial: Actor Robert Downey Jr is virtually unrecognisble in the trailer for his new film Tropic Thunder

Action man: Robert wore a wig and make-up for the part

Downey Jr plays a worthy Oscar-winning actor taking on a role originally written for a black actor, and rather than re-write the part, he goes method.

The star studded cast includes comedians Ben Stiller, Jack Black and Alan Partridge star Steve Coogan.

Clearing anticipating a backlash, Downey Jr told a US magazine: "If it's done right, it could be the type of role you called Peter Sellers to do 35 years ago. If you don't do it right, we're going to hell."

Downey explained that he kept the character from becoming a caricature because he "dove in with both feet."

"If I didn't feel it was morally sound," he said, "or that it would be easily misinterpreted that I'm just C. Thomas Howell in ("Soul Man"), I would've stayed home."

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Transformation: Downey Jr. plays overly committed actor Kirk Lazarus, a white man cast to play a black soldier in the satire

The film centres on a group of pompous actors making the most expensive Vietnam war movie ever made.

Fed up with their self-involved cast, the film's makers drop them into the jungle to take care of themselves, where they get caught up in a conflict they don't realise is real.

The cast also includes Steve Coogan, Nick Nolte and cameos from Tom Cruise and Tobey Maguire.

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All guns blazing: as well as starring in the film, Ben Stiller co-wrote, directed and produced it

Funny man: the cast also includesAlan Partridge star Steve Coogan

"I had no idea how people would respond to it," Stiller told the magazine. But at a recent screening, black viewers liked the film, he said.

The film, Stiller's first as director since Zoolander, also sees his character adopt an Asian baby but worries "that all the good ones have gone".

Paramount is set to release 'Tropic Thunder' in the U.S. on 15 August.

Unrecognisable: of the controversial role, the actor said: 'if you don't do it right, we're going to hell'