We've had little more than some concept art and casting news for GUARDIANS, which is just about to go in front of the lens, and there's been a lot of speculation about the villains in the film. Thanos has long been speculated to be the frontrunner, but with a main "henchman" that does the heavy lifting, such as Phalanx, The Controller, or The Collector.
According to our source the main villain will in fact be Ronan the Accuser, the ruler of the alien race known as the Kree. Ronan has fought the likes of the Fantastic Four, The Inhumans, and Guardians of the Galaxy in the comics and is a mainstay of the Marvel cosmic universe, so it's well in line for him to be featured as the main villain, especially with Marvel looking to expand it's cinematic adventures to the far reaches of space. Could this be a lead-up to the Kree-Skrull war in THE AVENGERS 2? It's anyone's guess, but Ronan is certainly a formidable threat and a solid lead villain for GUARDIANS OF THE GALAXY.
Actor Lee Pace was recently cast as a "villain" in the film, but it's hard to say if it's for Ronan the Accuser. There's nothing to say that he couldn't be playing the other rumored villains, but if he's playing the lead, then he's playing Ronan if our source is correct.