4. Magneto
Another X-men character who has been brilliantly cast on multiple occasions, Magneto was played in the first three X-Men movies by legendary actor Ian McKellan who, similar to Patrick Stewart with Professor X, lent a certain class to the role. Even though McKellan's Magneto was a straight up bad guy, he was much more nuanced and sympathetic, due to his childhood years in the Holocaust, than your average super-villain. For X-Men: First Class, the role was given to Michael Fassbender who might be even better in the role than McKellan was. Fassbender's Magneto is a complicated character. More an anti-hero than a villain, this incarnation is also someone with a tortured past who spends years looking for revenge. Once again, with the upcoming X-Men: Days of Future Past, Fassbender and McKellan will both appear as Magneto, and hopefully the people in charge can find a way to get them both onscreen together.