Den of Geek are citing “solid” sources and claiming they know who will be in the film. According to them Benicio del Toro will be playing The Collector, Lee Pace will be Ronan The Accuser and Karen Gillan will play Nebula.
The Collector is one of the oldest characters you can encounter in the Marvel universe, an Elder who – as the name suggests – collects obsessively in order to save things. He’s tried to collect The Avengers on a few occasions and has even been happy to see Earth ravished so he can collect the survivors. The Collector has a limited ability to see the future and has seen the threat that Thanos is. Thanos, of course, was the super villain hinted at the very end of The Avengers movie.
Meanwhile, Ronan The Accuser started out life as a straight up villain in the Marvel universe; an enforcer for the alien Kree race, but has slowly become more heroic and level headed. An alien Judge Dredd? Something like that.
Karen Gillan’s Nebula is a space pirate who has claimed to be the granddaughter of Thanos. This is an interesting one as Nebula has battled both Ronan The Accuser and Thanos before. She’s certainly a villain.
Via Den of Geek.