We got our first look at Thanos (aka The Mad Titan, Avatar of Death) in a tag scene at the end of The Avengers, strongly suggesting that the Marvel villain would be making appearances in future films.  Now, we have word that none other than Josh Brolin is set to voice the big bad.  Fans will likely get their next look at (and listen to) Thanos in James Gunn's Guardians of the Galaxy, which greatly expands the current Marvel Cinematic Universe beyond its terrestrial boundaries.  Logic follows that a villain of Thanos' proportions (he's got god-like powers and has attempted to wipe out the human race) would also appear in future films like Avengers: Age of Ultron, with The Avengers 3 a likely place to feature the antagonist.  Hit the jump for more.

Latino-Review reports

that Brolin will be voicing Thanos in Guardians of the Galaxy, with confirmation coming via Variety.  They're reporting that Thanos is also expected to appear in Avengers: Age of Ultron, which was corroborated by The Wrap.  While journos are in accord about the Guardians appearance of Thanos, HitFix's Drew McWeeny had the following to say in response:

‏@DrewAtHitFix He's not in "Age Of Ultron." None of the stuff from the "Guardians" end of the galaxy is yet. That's Phase 3.

The Mad Titan is expected to show up in the third act of the space-based actioner opening August 1st.  Here's an idea of what that scene may look like, from an earlier article discussing Kevin Feige's work with Gunn on the picture:

Gunn freezes a frame of an imposing-looking villain any serious comic book fan would recognize instantly. He sits on a rocket-powered throne. Feige sees something on the screen that he doesn’t like. The evildoer needs to be farther away in the frame so he looks more imperious, he says.

“I don’t know,” says Gunn. “I think it’s going to look cool, man.”

“You just don’t want him to feel petty in that way,” Feige says. “I think it’s a fine line.”

“How do you think it comes off as petty here?” Gunn says.

“He’s so damn close,” Feige says.

“Yeah,” concedes Gunn. “I think I’m going to have him floating in space.”

Feige is concerned about the throne, too. He points at the base. “Those don’t need to be rockets,” he says. “Maybe gravity disks?” Feige says he’ll check back later.

In the hallway he extracts a pledge not to name the bad guy. “That could not be a bigger spoiler,” Feige says.

Since the tag in The Avengers, and probably well before that, Feige and Marvel have been planning big things for the big bad.  Here's what Feige had to say a couple of years ago when the scene originally played out for audiences:

“Clearly, there’s a purpose to us putting him in the end of that movie. We do have plans for him. I wouldn’t say we ever feel the need to rush anything one way or the other. We succeeded in Phase One because we stuck to our guns and stuck to the plan. That plan took place over many, many years and it ultimately paid off. I see Phase Two unfolding in the same way of us taking our time, us doing what’s right for each individual movie, while folding in elements that will not only build up to the culmination of Phase Two, but even Phase Three.”

Though Whedon and Marvel cast actor/stuntman Damion Poitier to portray the baddie at the end of The Avengers, Feige admitted they'd recast the role when he reappears:

“I think we feel pretty free to recast. That was cast for literally that one shot. Depending on what the role requires from future movies, we’ll go from there.”

Looks like Brolin is what the role required.  You'll get your first look and listen in Guardians of the Galaxy when it opens August 1st.