The Avengers have fought a number of villains over the years. They fought villains that range from being humans to gods, to robots to aliens as well as mutants. Here is what I want to be sure on. Do they have an arch-enemy or arch-nemesis? The X-Men have Magneto and his brotherhood of Mutants, the Fantastic Four have Doctor Doom, the Green Lantern Corps have Sinestro, Teen Titans have Deathstroke and the Justice League have the Legion of Doom in the cartoons. Basically those teams either have one guy or a group of bad guys as a nemesis.
If the Avengers don't have an offical nemesis, I can think of a number of villains that could possibly fit the bill. I think Ultron, Thanos, Loki Masters of Evil or the Dark Avengers could qualify to be their nemesis.
Ultron was created by one of the founding members of the Avengers that went rogue and tries to kill them. The guy has a very personal connection to the team since he was created to help but basically said screw that. His "Father" is Hank Pym and he did create Vision a member of the Avengers.
Thanos is an alien titan that have fought the Avengers a number of times so he can be with Death and has use the infinity gems to defeat them or help achieve his goals.
Loki is the God of Mischeif and Thor's arch-rivial. He is the very reason the Avengers are around to begin with.
The Masters of Evil can most likely be seen as the Avengers arch-nemesis. They first appeared in The Avengers #6, and ever since then, they have been a recurring enemy. Some of the members have a some connection to one of the heroes on the Avengers like Baron Zemo and Captain America. Their main goal is to take over the world and the Avengers are there to stop them. At one point, the Masters of Evil were the Thunderbolts that were suppose to win the hearts of the public so Baron Zemo can take over the world.
The Dark Avengers can be seen as an arch-nemesis to the New Avengers and the Mighty Avengers during the Dark Regin and Siege. The members of the Dark Avengers are usually villains posing as heroes like the original Thunderbolts. The first group of Dark Avengers were villains that had some kind of connection to the New Avengers. Osborn and Venom with Spidey, Daken & Wolverine, eventually Moonstone & Ms. Marvel.
What do you guys think? I know these arguements aren't that good, but I tried to touch at least one reason why one of these guys can be labelled as the Avengers nemesis.