[Update: Watch all 5 Guardians of the Galaxy character introductions here.]

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Marvel is going full speed ahead with its Guardians of the Galaxy promotional campaign this week, starting with a first full trailer for the "Cosmic Avengers" space adventure, which was, admittedly, scant on a few key details. The biggest omission that fans noticed was the lack of dialogue from CGI characters Rocket Raccoon and Groot, who have A-list stars voicing them in Bradley Cooper and Vin Diesel, respectively.

Obviously one of the mysteries has now been solved; you can hear Bradley Cooper laying down voice work for the character in the featurette above. A second video (see below) introduces Vin Diesel's Groot - but does NOT include the Fast & Furious star delivering Groot's one and only speakable phrase, "I am Groot."

As you can see in the video above, the line of dialogue is brief, but telling. When Cooper was first cast as Rocket, fans were understandably surprised that pretty-boy leading man from The Hangover series would be the perfect fit for a militant raccoon-looking space alien; this was a character that many thought would be best served by the voice of Jason Statham, after all....

However, the Internet quickly dug up old archive footage of Cooper showing off some pretty impressive voice manipulation/impression skills, which led to the question of whether the star's own tones would be used for the character, or whether he would be creating a special voice for the performance. Judging from the video, I'd say it's a bit of both?

Guardians of the Galaxy Official Photo - Rocket Raccoon in Prison Lineup
CLICK IMAGE FOR LARGER VERSION

Cooper looks to be using a more grizzled (smoke-ravaged) version of his own voice, complete with that slight accented edge that I personally know hails from the city of Philadelphia (where Cooper is from). It's not enough accent to raise questions about a space creature with a uniquely earth-inspired accent (like a Cockney accent might have), but it's enough to make Rocket sound edgy and feisty and believably tough in a prison setting. The fact that the scene of a miniature Raccoon guy talking tough in the middle of space prison sounds at all believable is a big win for director James Gunn and Cooper, far as I'm concerned. And the Raccoon guy said "booty." That's just a funny little cherry on top...

I've already gone on record as saying I think this particular voice casting is "high school smart." What I mean is: Casting a heartthrob like Bradley Cooper in the role of a cute furry animal character is a pretty strong way to lure in a female crowd that might otherwise brush this crazy Marvel Comics space movie off as silly geek stuff. It's pretty much like getting the high school quarterback to endorse your science fair, so that all the popular girls show up. Hence the term, "high school smart."

Guardians of the Galaxy Official Trailer

Guardians of the Galaxy is directed by James Gunn off of his script co-written by Nicole Perlman. The film stars Chris Pratt, Zoe Saldana, Dave Bautista, Lee Pace, Michael Rooker Karen Gillan, Djimon Hounsou, Benicio del Toro, John C. Reilly, Bradley Cooper, Vin Diesel and Glenn Close.

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Captain America: The Winter Soldier hits theaters April 4, 2014, Guardians of the Galaxy on August 1, 2014The Avengers: Age of Ultron on May 1, 2015, Ant-Man on July 31, 2015, and unannounced films for May 6 2016, July 8 2016 and May 5 2017.