The Avengers just went up against their toughest foe yet in Thanos, but if you thought Thanos was tough, you'll be surprised to find that he's nowhere near the top of the list. If one of these characters interests you I encourage you to further research because I am going to be 50% jokes and 50% facts. You have been warned. I don't have a Bachelor's degree in Marvel, after all (I have four more years at Brown), but I do know my Marvel characters. Check it out - #1 is a total beast, and the most powerful hands down.
