There's one major Marvel Character in Guardians of the Galaxy that hasn't even been teased in any of the official trailers or stills, and that's Thanos, the big bad guy of the Marvel films.
Thanos made his first appearance onscreen (played by Damion Poitier) at the end of The Avengers, giving an insidious smile when told that attacking Earth is courting death. Or "Death," with a capital D, as the comic book Titan is in love with the physical embodiment of Death.
Thanos is a member of The Eternals, a group of god-like beings with immense power, far beyond that of humans. Thanos is referred to as the “Mad Titan” in the comics for attempting to wipe out the entire human race with his Infinity Gauntlet, capable of manipulating, time, space, reality and even the human soul.
We don't know how big Thanos' plan is, but we know from Thor: The Dark World that The Collector is collecting powerful mystical objects that most speculate will make up the Marvel Cinematic Universe's version of the Infinity Gauntlet. If the Gauntlet is coming to screen, so is Thanos.
An article on James Gunn's post-production process reported a scene with Thanos on a rocket throne in Act 3, which suggests an appearance long enough that someone is going to have to voice the Mad Titan, someone that could take the part into Avengers 3 as a major villain.
That meant Marvel was looking for an actor of some caliber, someone that could give a performance to a very complex, but very purple-skinned alien villain.
Our sources tell us that person is JOSH BROLIN!!
He'll be providing the voice of Thanos in Guardians of the Galaxy and with a name and reputation like that, it's likely he'll join James Spader and Tom Hiddleston as actors who have tried to kill The Avengers.
We reached out to Brolin's representatives at CAA and they're giving us the run around.
Latino Review and Variety confirms it too