Ben Stiller has praised Robert Downey Jr’s performance in new movie Tropic Thunder, calling him a “genius”.

“He’s brilliant,” Ben told Access Hollywood. “I think he’s probably one of the best actors I’ve ever worked with, if not the best.”

Robert plays Australian method actor Kirk Lazarus, who goes to great lengths, including pigmenting his skin, to play an African American in a Vietnam war movie.

Ben, who co-wrote, directed and stars in the comedy movie, said:“I just think it’s amazing seeing him have the respect and success at this point in his life after everything he’s been through.”