4. Fin Fang Foom
Although I'm not overly keen on the character in the comics, I imagine that an on-screen version of Fin Fang Foom could be great in a movie - both visually and as a potentially huge future challenge for Iron Man. The Iron Man movies have been a massive success, with the third instalment smashing the box office proceeds of those before it and grossing over a billion dollars, but never has Tony Stark had to go up against such a monstrous foe on his own. The slow-moving Leviathans that he went up against alongside his Avengers team-mates were big and caused a lot of collateral damage, but they didn't have much else going for them and Hulk and Thor dealt with them relatively easily. Foom however, is a giant and highly intelligent dragon with regenerative abilities and the ability to fire a combustible acid mist from his mouth and would be a different prospect altogether. And seeing Foom going up against Stark on screen would surely be a sight to behold. He has links to the Mandarin, which could be explored as well, and would make for an interesting movie twist should Marvel choose to rectify the discontent that the poor Mandarin interpretation from Iron Man 3 brought amongst fans. Although Foom is a classic Iron Man villain, he is so far removed from anything seen before in an Iron Man movie that it would indeed be quite surprising to see him. So, mainly for the potentially outstanding visuals, Fin Fang Foom would be a great addition to the Marvel Cinematic Universe and would be wonderful to see in Iron Man 4. Although Foom was discovered sleeping on Earth in the comics, a flashback scene of him in space approaching Earth in ancient times from his home planet of Maklu IV would be great.