Thanos is a villain who we're about to see make a big impact in the Marvel Cinematic Universe, but he's been causing the comic book version of The Avengers problems for decades. Not convinced? Well, the Mad Titan holds the honour of being one of the few villains to have actually killed Earth's Mightiest Heroes, wiping them, the X-Men, and half the universe out in one fell swoop when he got the Infinity Gauntlet. His daughter Nebula may have undone that, but it makes his achievements no less great. Obsessed with death and massively powerful even without that cosmic weapon, there's not a single member of The Avengers who have fared well in a one on one battle with this villain, and while the team has managed to defeat him, Thanos has yet to be stopped for good and continues to seek out those all-powerful Infinity Gems.
