A big name actor has been named to voice Thanos in upcoming Marvel films.  Josh Brolin has been cast as Thanos for Guardians of the Galaxy, according to Latino Review, and will have an even more significant role as the character in Avengers: Age of Ultron, according to The Wrap.
 
Thanos made a brief appearance in a post-credits scene in The Avengers, played by Damion Poitier, and the god-like member of the Eternals had already been announced as a character in Guardians of the Galaxy (see "Thanos Role Is Cast").
 
Brolin can also be seen this summer playing Dwight in Sin City: A Dame to Kill For (see "Character Posters for 'Sin City: A Dame to Kill For'").