Who he is: Thanos, a.k.a. The Dark Lord, a.k.a. The Mad Titan
His power: It’s unclear. He’s a big guy and seems to instill fear in just about everyone, but so far we haven’t seen him flex his muscles, so to speak. (Though, based on the comic source material, he seems pretty indestructible.)
His story: Thanos’ first appearance is in the post-credits stinger of The Avengers, where he reacts to the news that Earth has proven itself incapable of being conquered—and that to attempt it would be “to court death”—with a smile. His next appearance comes in Guardians Of The Galaxy, where we learn Thanos (or “The Mad Titan” to his enemies or unhappy collaborators) has raised two adopted daughters, Nebula and Gamora, and trained them to be powerful assassins. He cuts a deal with the Kree zealot Ronan The Accuser to steal an orb for him, which contains one of six infinity stones. However, Ronan betrays him, intending to keep the stone for himself, but is destroyed by the Guardians after a battle above the planet Xandar. Thus, in the credits scene of Avengers: Age Of Ultron, Thanos is shown putting on a gauntlet that holds spots for each stone, saying, “Fine… I’ll do it myself.”
Played by: Josh Brolin, though the on-set actor filmed for The Avengers was Damion Poitier, and James Gunn similarly did on-set coverage for the character in Guardians Of The Galaxy, despite Brolin’s motion-capture performance.
Currently, Thanos is: Seemingly prepared to unleash holy hell.
Where will we see him next? He might have a cameo in upcoming films, but he’s confirmed as the central villain in Avengers: Infinity War.