Ben Stiller has praised his Tropic Thunder co-star Robert Downey Jr, career him a 'genius'.
Speaking to Access Hollywood, Stiller aforementioned of the Iron Man star: "He's brilliant. I think he's probably one of the best actors I've ever worked with, if non the best".
Stiller and Downey Jr are joined by a turn of high profile comedians in the Vietnam war pic spoof, including Jack Black and Steve Coogan.
But it's Downey Jr's portrayal of Kirk Lazarus, an doer who goes to uttermost lengths to acquire a part in the film, including pigmenting his skin so he can play an African American, which draws the greatest praise from Stiller.
"I'm having this experience of watching him and improvize and take this character which isn't an easy proposition to make this guy relatable, and he's just amazing," he said.
"I just think it's astonishing seeing him have the respect and success at this point in his life afterward everything he's been through. He deserves it. So I was really excited to crop with him."
Stiller, who co-wrote, directed and stars in the photographic film admits the character could potentially be seen as being controversial.
"I felt up we had to be really authorise about what our point of horizon was where the mood was climax from with this motion picture," he added.
"We were satirising actors and the lengths actors go to for recognition and attention."
Tropic Thunder is released in the UK on September 19th.
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