Magneto has long been seen as the main antagonist of the X-Men mythos yet his Ultimate Marvel counterpart took this to a new level - unlike the more anti-hero Magneto most X-Men fans know from the "mainstream" series the Ultimate version of Magneto was dark, cynical and sought to utterly dominate humanity (who he refered to as "insects") - he also openly called for genocide on more than one occassion. This stands as a contrast to the mainstream Magneto who only seeked to rule over humanity by his own moral beliefs and has at times attempted to follow the peaceful ideals of human/mutant coexistence embodied by his on/off enemies, though he frequently returns to his darker path in life.
His monstrous actions ultimately culminated in the much reviled Ultimatum series in which he stole Thor's hammer Mjolnier and used it to cause planet wide devestation causing millions of deaths and he personally murdered many heroes including Charles Xavier and Wolverine before he was in the end killed by Cyclops while Magneto himself decided he was beyond redemption, accepting his fate. His actions here, along with the disbandement of the X-men due to the death's of so many of their members leaving them no longer capable of influencing public opinion, meant anti mutant sentiment worsened astranomically to a much worse extent even than in the mainstream universe.
The X-Men movie mythology borrowed heavily from the Ultimate comics rather than the "mainstream" and thus the movie version of Magneto can be seen as having a lot of the personality traits of the Ultimate Magneto (which explains why he was willing to commit mass genocide in that film, seemingly in contrast with what most X-Men fans believe to be Magneto's character).