(CBR)  Marvel has gathered a stellar cast for director James Gunn’s space adventure "Guardians of the Galaxy": Glenn Close, John C. Reilly, Benicio del Toro, Zoe Saldana, Karen Gillan, Chris Pratt, Lee Pace, Michael Rooker, Djimon Hounsou, Dave Bautista … Vin Diesel, most likely.

While the actors have most of the key roles covered, there’s still one yet to be filled: Rocket Raccoon. However, The Hollywood Reporter cites sources that confirm Bradley Cooper is in talks to voice Rocket Raccoon. In addition to Cooper’s role in “Guardians of the Galaxy,” THR’s sources further confirm that Elizabeth Olsen is currently in negotiations to join “The Avengers: Age of Ultron” as the Scarlet Witch.

The site contends Marvel has made an offer to Academy Award nominee Bradley Cooper to voice the fan-favorite character.

"Guardians of the Galaxy" is filming now in London ahead of an Aug. 1, 2014 release.

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