'Avengers' Aliens: Yup, They're... [Spoiler Alert]

They're Skrulls. Says Joss Whedon:

"The alien race are the Chitauri -- or a version of them -- because they are not one of the key races and they don’t have a storied history. That wasn’t the point. I know this debate will go on long after I’m dead. I would say it was the Kree-Skrull race."