Archenemy, arch-rival, arch-nemesis whatever you want to call it, it's personal. The yin to the yang, the polar opposite, that villain that stands for all that you stand against.
Polarity in comics is important, without clear and dangerous evil there can be no altruistic and noble good. We need the dark to appreciate the light.
Oftentimes a hero's arch-nemesis reflects their own beliefs and/or their own psyche. Venom works as Spider-Man's antithesis because he has very similar powers and beliefs to Spider-Man himself but uses them in a way that Spidey never would. You wouldn't catch your friendly neighborhood Spider-Man EATING the neighbors for one.
Keep in mind, these are comic history's major rivalries and there can be only one per superhero (sorry, that means no Venom or Galactus).These baddies may overlap other Marvel properties, but there really is only one main rivalry they are known for. They represent the epic confrontations, the big bads, the best arch-enemies in Marvel Comics.
Make sure to vote-up your favorite Archenemies from the Marvel Comic Universe!
Archenemy of: Charles Xavier/X-Men