He's well-known for playing Tony Stark (Iron Man) and of course Sherlock Holmes. Actually those are not my two favourite Robert Downey Jr performances, although they do come very close.
My first is when he was in Ally McBeal and second the very underrated film; Kiss Kiss Bang Bang. Downey will next be on our cinema screens in The Judge. In 2015 there will be the next Avengers (Assemble) film - yay!