5. Ezekiel "Zeke" Stane
Having defeated the traitorous Obadiah Stane in his Iron Monger suit in the first Iron Man movie, one idea Marvel could utilise with Iron Man 4 is the revenge angle. In the comic books, Ezekiel "Zeke" Stane is Obadiah's son. He has been building bio-weaponry and manufacturing next-generation weapons for terrorists and supervillains since he was only nine years old. Utilising his skills, he creates a suit that is actually physically attached to his anatomy. In this sense, he is a sort of cross between Iron Man and the Aldrich Killian character we saw in Iron Man 3 - he is armoured, but by virtue of an actual biological upgrade. What a surprise it would be for the cocky Tony Stark - a man who has saved the world from an alien threat - to find himself tackling a young upstart whose technology is superior to the equipment he has relied upon for so long. The fact that Zeke would have a revenge motive would only add to the story and I think he would make a great on-screen villain for Iron Man - played by Robert Downey Jr. or otherwise.