5. Namor
Ever since Atlantis was highlighted on a map in Iron Man 2, rumours of Namor the Sub-Mariner's potential appearance in the Marvel Cinematic Universe have been rife. A sea-dwelling Atlantean/Human Mutant hybrid with flight abilities, superhuman strength and durability, Namor is a monarch of Atlantis who first appeared as more of a villain but emerged from the depths of the ocean to aid the allies in the fight against Adolf Hitler in World War II. A solo Namor movie could occur before Avengers 3 but, even if that doesn't happen, it wouldn't take much to introduce him, given that the nature of the events of Infinity Gauntlet attract heroes from around the globe to form a defence against Thanos. The disappearance of some members of his family - thanks to Thanos' "vanish" trick - could be the stimulus for Namor to head to the land, which would draw attention from the likes of S.H.I.E.L.D., who could explain what was going on to Namor, leading to him joining the other heroes. Namor was present in the final fight against Thanos in the Infinity Gauntlet comic arc and, given his wise nature, he could form part of the team of people who confer about the plan of action (along with the aforementioned Doctor Strange and Pip the Troll et al). Essentially, there's definitely a potential role for Namor in this movie, should Marvel want to give him one.