While Vin Diesel and Bradley Cooper were recently revealed to be voicing Groot and Rocket Racoon respectively, many other actors have been rumored to appear in Guardians of the Galaxy, whether in main or supporting roles, like Steve Agee, Stephen Blakehart, and Sean Gunn. When Directer James Gunn was (for some reason) asked why cast members weren't included on the unreliable IMDb for Guardians of the Galaxy, he clarified a few casting rumors involving supporting roles.
IMDb is not always correct. Even right now I believe it contains misinformation. A complete cast list will not be released until closer before release- and we are not currently releasing a list of all the characters in the film, answered Gunn.
That said, Stephen Blackehart and my brother Sean are in the film but my good friend Steve Agee is unfortunately not. Although he would make a great Thanos.
In fact, despite the rumors, Steve Agee did not even audition for the film. Gunn revealed,
Besides my brother and Gregg Henry, and a couple of others, we pretty much cast all of the supporting roles out of England. There’s a lot of take there, so it wasn’t hard! I love working with Steve, though – he’s a great friend and an incredibly funny guy.
“Guardians of the Galaxy,” the next epic adventure from Marvel Studios, is directed by James Gunn from his screenplay, with a story by Nicole Perlman and Gunn, and the film will introduce audiences to a whole new side of the Marvel Cinematic Universe. The all-star cast includes Chris Pratt as Peter Quill aka Star-Lord, Zoe Saldana as Gamora, Dave Bautista as Drax the Destroyer, Lee Pace as Ronan the Accuser, Michael Rooker as Yondu, Karen Gillan as Nebula, two-time Academy Award nominee Djimon Hounsou as Korath, Academy Award® winner Benicio del Toro as The Collector, Academy Award nominee John C. Reilly as Rhomann Dey, and six-time Academy Award nominee Glenn Close as Nova Prime. Marvel’s “Guardians of the Galaxy” is slated for August 1, 2014!