5. The Red Skull
I think if there's one thing fans of this franchise can agree on it's that other than Tom Hiddleson's Loki the best villain of Phase One was without a doubt Hugo Weaving's Red Skull. Everything about him was spot on - from the look to the superiority complex to the use of Weaving's best Werner Herzog impression for the voice. Hugo Weaving brought Captain America's greatest spoil to life, and it's a damn shame that he hasn't been brought back to tussle with Earth's Mightiest Heroes. In fact, an Avengers vs. Red Skull brawl for the sequel would have been a great idea. For those paying close attention to the end of Captain America: The First Avenger, it's pretty clear that Johann Schmidt didn't meet his demise at the hands of The Tesseract but was instead transported to a realm unknown. And therein rests the possibility for a grand return. Imagine the Skull sacking Asgard to reclaim The Tesseract and returning to Earth as a conqueror out of time? Or even something as simple as returning to lead a resurgence of HYDRA? Obviously The First Avenger was written open-endedly to allow for the Red Skull's return, and such a return would have made a great second chapter to the saga of The Avengers. And as far as the force that would assist him in his fight just as easily as it could be HYDRA there was another possibility that would have worked just as well....