It's been the speculation of the century ever since we saw The Mad Titan grace the screens during the mid-credit scene for The Avengers. It was preformed by stand in actor Damon Poitier but he never spoke. Now Latino-Review finally has gotten a scoop on who may actually play Thanos himself.
According to their sources non other then Josh Brolin (Oldboy, Gangster Squad) will lend his voice in Guardians of the Galaxy. Which only assumes that we will see The Mad Titan off screen speaking to Ronan the Accuser (Lee Pace). Now while he is simply lending his voice for Guardians of the Galaxy do not count him out in acting out the role as well when The Avengers 3 comes around in 2018ish. First, The Avengers need to reassemble to battle Ultron voiced by James Spader in The Avengers: Age of Ultron!
The Wrap has confirmed he will voice Thanos! Also adds Josh Brolin will make an appearnce in The Avengers: Age of Ultron and acutally has a bigger role in that film than Guardians of the Galaxy
Guardians of the Galaxy hits this August; The Avengers 3 release date is TBA