The Marvel panel has just wrapped at Comic-Con, and Marvel dropped a ton of news, but not what everybody was expecting. Introducing the Guardians of the Galaxy cast, Marvel Studios President Kevin Feige confirmed that Djimon Hounsou is playing Korath the Pursuer, a cybernetic member of the alien Kree empire and typically an ally of Ronan the Accuser, who will be played by Lee Pace. Hounsou leaked that Korath will be an ally of Thanos in the film, but who knows if that's going to hold up. Also confirmed was Karen Gillan as Nebula, a space pirate and potentially Thanos' granddaughter. Benicio Del Toro will also play the Elder of the Universe known as The Collector, the first to recognize the threat of Thanos.
The big news came right at the end, as Joss Whedon hit the stage floor right at the end of the show, and teased a promo video. The footage featured a metal object being pounded from all sides, with prophetic words in the background about the team's demise. But then the object revolves, and it's revealed to be the face of Ultron, the android enemy of the Avengers, created by Hank "Ant-Man" Pym. The title of the film was then revealed to be The Avengers: Age of Ultron, arriving in the summer of 2015.
So the big news to take from this is that it will be Ultron in The Avengers sequel, and not Thanos. It looks like Thanos will be appearing in Guardians of the Galaxy, which makes sense considering every character has close ties to him. Age of Ultron is also a fairly recent Marvel comics crossover storyline, only completing about a month ago. It had Wolverine going back in time to kill Hank Pym before he could create Ultron, because in the present the android has wiped out nearly all of the superheroes. It's a storyline that closely resembles Xmen: Days of Future Past, ironically.