But the amazingly resilient actor is only 49 as of today—a very happy birthday to you, sir!—and we thought it a perfect time to take a look back at the incredibly successful decade the movie star has had.
Downey, who went through the personal ringer in his 30s, only to bounce back better than ever in his 40s, has never been shy about giving shout-outs to his own troubled past.
Accepting the Kids' Choice Award for Favorite Male Buttkicker last Saturday, the actor told the adoring crowd: "This is the highest honor yet bestowed on me—I'm grateful, humble, the whole deal. You know I wasn't always a buttkicker. In fact, life has kicked my proverbial butt countless times in many ways for many years, until I decided one day to start kicking back. Now look at me!"
Both his candor and his irrepressible tongue-in-cheek (well, for the most part) self-congratulatory ways have really only served to make him more likable. But of course, none of that would matter if he didn't also walk the walk on the big screen.
Here are five roles that defined a decade for Downey:
1. Iron Man: Well, of course this is the role—which Downey actually had to audition for, remember?—that changed everything. So much about that role—and we're including the two sequels, The Avengers and the upcoming Avengers: The Age of Ultron in that as well—just wouldn't have worked if he wasn't Tony Stark. Asked in a recent Q&A with Variety whether he was nervous about taking on the role, Downey said, "Nervous? I was begging. I was absolutely certain it would change my life." His instincts were sound.
2. Tropic Thunder: Downey was nominated for a Best Supporting Actor Oscar in 2009 for playing over-the-top Australian method actor Kirk Lazarus, who actually has surgery to darken his skin so that he can better play a black man, in the Ben Stiller-directed satire about the movie-making process.
3. Zodiac: Downey played a hard-living crime reporter in the underrated David Fincher film about the 1960s- and 1970s-era serial killer that terrorized the San Francisco Bay Area. The actor was his usual self—sardonic, quick-witted and crafty. And he stole every scene he was in.
4. Sherlock Holmes: He was already huge again, thanks to Iron Man, and the only thing that kept Downey from being the Sherlock of a generation was that other fellow who's doing such a bang-up job for the BBC. The sequel was pretty ridiculous, the first of Guy Ritchie's pair of films, costarring Jude Law as Dr. Watson, was action-packed and a perfect showcase for Downey's considerable charm and lovable eccentricities.
5. Kiss Kiss Bang Bang: The violent crime caper remains a favorite of both hard-core Downey fans and those who just like talky, mantastic dark comedies, and it marked his first collaboration with director Shane Black, who cowrote and directed Iron Man 3. He plays a thief who unwittingly impresses a producer when he stumbles into an audition while fleeing the scene of a burglary. When he meets the P.I. hired to help coach the "actor," he ends up in way over his head—quite hilariously at times—and running for his life.
And we sure do hope that Chef, coming out May 9 and reuniting Downey and original Iron Man visionary Jon Favreau, is another addition to the fab-in-his-40s canon.
Happy birthday, RDJ!