3. Ultron
2013's first major comics event was Marvel's Age of Ultron which saw Earth's Mightiest Heroes defeated after a massive attack from Ultron from the future - caught them off guard. As they struggled to marshal their forces and defeat Ultron's numerous drones, Wolverine and Sue Storm decided upon a hail Mary, all or nothing attempt to reverse the chaos go back in time and kill Ultron's creator, Hank Pym! The plan worked but, as is always the case with time travel, once they changed one thing in the past, the future was changed in unforeseen ways too. Returning to a world where a cyborg Tony Stark ruled over everything, Wolverine and Sue decided to go back again and try a better plan: getting Hank to build a failsafe into Ultron. This time it worked and the Avengers were able to defeat Ultron but the time travel was too much for time itself! Time tore causing major ripples across the Marvel Universe with new characters appearing in different places and a massive threat to the Ultimates Universe emerging. Despite the many problems with the Event, the final battle against Ultron wasn't bad as Earth's Mightiest Heroes went up against the killer robot one last time. But after all that, Ultron was done, right? He wouldn't return to become a threat again? Well, shortly after this Event ended, it was announced that The Avengers movie sequel would be subtitled Age of Ultron and, given Marvel's habit of releasing tie-in comics with their movies, I'd say it's a sure thing Ultron will be back before we know it.