For me, it's Robert Downey Jr.It wasn't terribly long ago that a superhero film role was the death knell of an actor. Today, not so much.
To me, it's Robert Redford. No other single actor lends more legitimacy to the superhero genre than Redford.
Who's your choice?
For a long time, Robert Downey Jr. was considered one of the best actors working in the business. Then he got into trouble. With Iron Man, he turned around not only his life's trajectory, but he was on the forefront of a paradigm shift in Hollywood.