A key figure in developing several characters in the cosmic side of the Marvel Comics universe, writer and artist Jim Starlin's works are quickly becoming a prominent part of the films as well. By the time The Avengers hit theaters in summer 2012, we had already seen a few of his creations at play - from the Infinity Gauntlet shown briefly in Thor, hidden away in Odin's Vault on Asgard, to the grinning Thanos in the mid-credits button of The Avengers. 'It's all connected' as the marketing slogan for Marvel's Agents of S.H.I.E.L.D. would remind us.
Later this year, we're going to meet at least several more of Starlin's characters in Guardians of the Galaxy, a film that will finally offer a little background on big bad Thanos and give moviegoers a reason to be keeping him in mind for future films. Starlin had mentioned last year at Montreal Comic-Con that Thanos was going to be coming back in not only Guardians of the Galaxy but The Avengers sequel as well, adding credence to theories that after we meet Star-Lord, Drax the Destroyer, Gamora, Groot, and Rocket Raccooon this August, they may make their way to Earth to meet the heroes we're already familiar with. Why else would the cosmic heroes and villains be introduced this year, right?
While the release schedule of the Phase 2 films may suggest something to that end occurring, we already know Joss Whedon's The Avengers: Age of Ultron is dealing with another new villain named Ultron (and his robotic army) instead. We don't know what new origin story Joss Whedon has come up with for Ultron (in the comics, Hank Pym aka Ant-Man created him), but for now we're going to assume it's Earth-based. Come time for The Avengers 3 however, and the Guardians of the Galaxy and the larger cosmos will definitely be involved.
So says GOTG writer and director James Gunn in an interview with EW.
"We're definitely connected to Avengers 3."
As for how? Look towards the Mad Titan we know as Thanos coming to Earth as the most likely reason. The character's been kept behind-the-scenes out in space throughout the events on Asgard and Earth we've seen take place in the Marvel Cinematic Universe to date, but we will see him again in Guardians of the Galaxy.
No voice actor has been cast yet to bring Thanos to life, or at least announced, but Gunn confirms that Thanos will be motion-captured and animated, just like Rocket Raccoon (voiced by Bradley Cooper) and Groot (Vin Diesel). Gunn describes Thanos' role in the villain hierarchy as the the "head of the snake." Expect Thanos to play a key role in Guardians of the Galaxy despite having what we expect to be minimal screentime as his henchman Ronan the Accuser (Lee Pace) steps up as the primary antagonist of the film.