During an interview, actor Clive Russell let slip an intriguing spoiler.
In the interview with Flicks and the City about his role in Thor: The Dark World, Russell had the following to say:
I worked with Benicio del Toro on a scene in which he was meant to be quite angry
Marvel announced months ago that good ol’ Mr. Mumbles would have a role in Guardians of the Galaxy, but what exactly that role is has not yet been announced (or even leaked). However, this certainly makes it seem as if his character is important enough to branch the gap between Thor: The Dark World and Guardians of the Galaxy.
The Collector? Thanos? He could be anyone… even you! No, not you. I’m sure you move your mouth when you speak.