Spoilers ahead for Avengers: Endgame. Without Robert Downey Jr., there is no Tony Stark, no Iron Man, and no Marvel Cinematic Universe. It's worth remembering that, a little over a decade ago, Marvel Studios (and Paramount Pictures) took a big swing with Iron Man, taking a less-than-marquee Marvel Comics character and giving it a shot at the big leagues. They also took a chance with RDJ, a critically acclaimed actor whose comedic chops in the 80s had been forgotten, replaced by personal problems and moderate success on TV and movies in the 90s and early 2000s. And …