The X-Men are one of the most legendary super teams in the history of cinema and comics. Back in a time where comic book movies were rare, they showed that they could be fun and profitable. Obviously, this was in no small part due to their iconic villain Magneto.
On the surface, Magneto may look like a typical villain. However, he is very much the product of his surroundings. As a young child he was in a concentration camp and witnessed unspeakable horrors. As an adult he lives in world bent on destroying people like him. Of all of the comic book villains, he is the only one you can find yourself rooting for and agreeing with. This is partially because he is based on civil rights leader Malcom X. As a result, Magneto is also one of the few villains to be completely justified in his approach. Humans have been waging war with mutants for his entire life, the fact that he wants to fight back is not so evil. Just like Dr.King and Malcom X, both the Professor and Magneto are fighting for the same thing, just in different ways. This rare occurrence is exactly what makes Magneto such an enticing villain and such an important part of cinema. The battle he wages with Professor X is unlike all other bad-guy good-guy relationships. While others fight over physical values, money, power, etc, they fight for morals and ideology. The question is not will good triumph over evil, it is how will it wind. At the center of the X-Men films and comics the true villain is humanly, Magneto is but a radical.
The X-Men films have shown this relationship perfectly with their constant references to a game of chess. Magneto and Charles are depicted as old friends, a common trope for arch rivals. However, they stand out because they remain friends through all of their battles and arguments. Both have a unique respect and appreciation for each other. It is this uniquely strange relationship that cements Magneto in cinematic history.