4. Loki
Tom Hiddleston's Loki has emerged as one of the more popular characters in the Marvel Cinematic Universe (along with Robert Downey Jr's Iron Man) and, in addition to the fact that he's also a classic comic book character, a movie focusing on him would be most welcome. Loki's origins were briefly explored in the Thor movie, but to explore them in full detail would be great. He is, of course, a Frost Giant who, because he was very small when he was born, was abandoned by his Father (the Frost Giant leader, King Laufey) and adopted by the Asgardian Allfather Odin, Laufey's sworn enemy. With Odin as his adopted Father, Loki was brought up as Thor's brother - as we have already seen on screen - but seeing the full extent of that story, the development of his magical powers and his slow descent in to being power-hungry and evil would make for a great movie and if Hiddleston would return to star in the adult portion of such a movie, there'd be a guaranteed hit on Marvel's hands.