Robert Downey Jr. has made it look too easy. Since the 2008 debut of his "Iron Man," Tony Stark, through a sequel and on into this weekend's big team-up blockbuster, the former hard-lucked bad boy has righted the ship and taken the reins of a character that has come to define him. It seems difficult to imagine Downey's career not including the gregarious, silver-tongued playboy/industrialist, but that he has conveyed the part with such ease betrays the skill needed to so absolutely define the character. As hard as it is to distinguish the actor's career from the role, it has become equally difficult to not think of Downey's interpretation when considering the 50-year-old staple of Marvel comics.