Kilowog is one of the alien members of the intergalactic police force known as the Green Lanterns, whom Ryan Reynold’s Hal Jordan is the most recent recruit of. He serves as the Corps’ trainer/drill-sergeant and will presumably be getting a fair amount of screen time in that role. Honestly, this is a great bit of casting, as I’ve always heard something close to Duncan’s voice whenever I read the character in the comics.
If it seems odd that the film is still adding cast members just a few months before its June 22 premier, it is probably due to the intensive amount of CG work that is still being finalized for the film. Recently, Oscar-winner Geoffrey Rush was announced as the voice of another CG-created alien Green Lantern, Tomar-Re.
Via Hollywood Reporter.