Which X-Men character was played by Ian McKellen and Michael Fassbender?

Magneto (Erik Lehnsherr) is a fictional character appearing in American comic books published by Marvel Comics, commonly in association with the X-Men. Created by writer Stan Lee and artist Jack Kirby, the character first appears in The X-Men #1 (cover-dated Sept. 1963) as an adversary of the X-Men.

Ian McKellen portrayed Magneto in five films of the X-Men film series, while Michael Fassbender portrayed a younger version of the character in four films.

The character is a powerful mutant, one of a fictional subspecies of humanity born with superhuman abilities, who has the ability to generate and control magnetic fields. Magneto regards mutants as evolutionarily superior to humans and rejects the possibility of peaceful human-mutant coexistence; he initially aimed to conquer the world to enable mutants, whom he refers to as homo superior, to replace humans as the dominant species. Writers have since fleshed out his origins and motivations, revealing him to be a Holocaust survivor whose extreme methods and cynical philosophy derive from his determination to protect mutants from suffering a similar fate at the hands of a world that fears and persecutes mutants.