11. Casting Tom Hiddleston as Loki
Hiddleston was a little-known British actor who had tried out for the lead in Thor. He didn't get the role, but the studio thought he might work as Loki, Thor's half-brother and nemesis. Boy, were they right: Marvel movies generally lacked strong villains until the Asgardian trickster came along. Hiddleston's complex, humorous and fierce performances in both Thor movies and The Avengers established him as a force to be reckoned with, and a bad guy whose sinister veneer hid a deeply conflicted and wounded individual.