Robert Downey Jr. is an actor at the top of his game — already a big-screen superhero, now an iconic super-sleuth.

He’s also surprisingly open about his self-doubt.

A charismatic performer with a sometimes troubled past, Downey struck box-office gold with 2008 hit “Iron Man,” and now plays the great Victorian detective in Guy Ritchie’s action-filled “Sherlock Holmes.” He knows he’s not many people’s mental image of the angular, cerebral and very British Holmes. He hasn’t let it stop him.

“You kind of act as if you’re up to the task until you find out whether you truly are or not,” said Downey, in a reflective mood during an interview in London.

“I was fortunate that right about this time last year I was really peaking in my own confidence and faith in my abilities. And seeing as I’d been cast and contracted and it was moving forward, it wasn’t like there was any benefit to me not thinking I was the perfect guy for it.”

Audiences will soon give their verdict on Downey’s muscular, street-wise take on the sleuth of Baker Street. The film has its world premiere in London on Monday and opens in the United States on Dec. 25. Continue…

December 13, 2009: Robert Downey Jr knocked out by stuntman on movie set