Who he is: Malekith, the Dark Elf
His power: Along with being an expert fighter, he possesses the superhuman strength and resilience of all Dark Elves. However, in Thor: The Dark World, he gains control of the Aether, a.k.a. the Reality Stone, which (temporarily) makes him one of the most powerful beings in the Nine Realms, stronger than even Thor.
His story: Malekith and the Dark Elves lost a battle with Odin and the Asgardians eons ago and went into suspended animation alongside his henchman Algrim and a number of surviving Elves. But when Dr. Jane Foster accidentally triggers the power of the Aether (and it takes possession of her body, slowly killing her), Malekith and his forces are awakened. He attacks Asgard but is prevented from acquiring the Aether by Thor, though he kills Thor’s mother, Frigga, in the fight. Wanting vengeance, Thor and Loki attempt to trick Malekith, but the Elf draws the Aether out of Jane’s body and into his own (while the transformed Algrim—now temporarily super strong and renamed Kurse—seems to murder Loki). Malekith plans to unleash the Aether in London during the Convergence (when portals between the Nine Realms are all in alignment), destroying other species in an effort to restore the Dark Elves to prominence. Instead, he gets his own ship dropped on him by Thor. Bad plan. R.I.P., Malekith.
Played by: Christopher Eccleston
Currently, Malekith is: Squashed like a bug.
Where will we see him next? He’s probably gone for good.