By now you should all know that Loki is the main villain in The Avengers. But who is that bad guy in the end credits of Marvel's Avengers? If you haven't seen the movie, stop reading this now, as spoilers follow.
Loki has an army from another dimension to help him take over the world, the Chitauri, who are from the Marvel Universe, just not the shapeshifting alien race from the comics.
I've had a few other suggestions in the comments below, and not all of them are Marvel, like Hell Boy (Dark Horse), Darkseid (DC), Apocalypse and Galactus (both Marvel), but it's none of them.
Which can leave only one villain, who is Thanos. He has the furrowed chin and the right colour skin, and is known to have had run in's with both Iron Man and Thor in the Marvel universe. As you can see, the comic art is a good fit for the face in the end credits.
Pretty sure this is the bad guy. What do you guys think? Comment below.