Tom Hiddleston as Loki at this year's San Diego's Comic Con. Kevin Winter/Getty Images At San Diego Comic Con this summer, there was no Q&A panel with the cast of Thor: The Dark World. There was only Loki, as Tom Hiddleston took the stage in full costume, demanded that the crowd "Say my name" and earn the kind of screams we associate with rock concerts that devolve into riots. It wasn't that they were trying to hide the Thor cast or shrug off the Comic Con crowd; it was that no combination of director Alan Taylor, star Chris Hemsworth or new footage could match the electric jolt of Loki on a rhetorical tear.

The movie itself, which is now out in theaters this Friday, is no different. Christopher Eccleston, a former Doctor Who and very memorable actor in his own right, is cast as the villainous dark elf Malekith, but under prosthetics and a digitally altered voice he's essentially background decoration. Loki, though not the main villain and actually working alongside Thor for much of the film, is not supposed to be the main focus, but he inevitably takes over anyway; the film picks up steam the moment the plot turns back to him, the dialogue crackles with extra verve when he and Thor spar together, and he gets every single one of the best jokes-- even the film's fantastic surprise cameo is thanks to Loki's trickery.

It's clear that Marvel realized they had something special in Hiddleston after the first Thor, bending over backwards to make him the primary antagonist in The Avengers (he needed a huge army of poorly defined CGI aliens to be a half-decent foe) and adding extra scenes with the trickster god during reshoots for Thor: The Dark World. It probably took all the restraint they had not to bring him back for Avengers: The Age of Ultron, but that restraint may be the only thing that saves them going forward. Loki is the best antagonist the Marvel Cinematic Universe has by far. He's also the only antagonist who's worth a damn. And that's going to be a problem if it doesn't change.

Disney / Marvel The caliber of the actors who have come and gone as Marvel villains is staggering-- Jeff Bridges won an Oscar after playing Obadiah Stane in Iron Man, Mickey Rourke nearly got one while shooting Iron Man 2, and Hugo Weaving, Guy Pearce, Tim Roth, Sam Rockwell and Ben mother-f'ing Kingsley (an Oscar winner too, of course) are all treasures in their own right. But every single one of them has gotten lost in the chaos of a movie that barely seemed like it needed them, the villains existing to wind up the action, pop up once in a while to provide a new threat, and get whaled on by the hero in the very end. You can make an argument for any of these actors in minor moments-- Sam Rockwell's suits as Justin Hammer, the phenomenal reveal of Kingsley's Mandarin-- but not a single one of them had motivations, or a story, that actually mattered to the plot. By the end of the movie all of them are sent on their way, either killed or out of power, and the deck is shuffled to allow the next Avenger to take on the next classy actor looking to build a vacation home.

Loki is the shrimpiest and in some ways least prepared of all the Marvel villains. His plot to take over the world in The Avengers, as everyone repeatedly tells him, is never going to succeed, and at heart he's motivated by the childish desire to get as much attention as his blond, heroic brother. But it's his puniness that gives him both his appeal and his staying power. He's power-mad, sure, but only in the way we all think we deserve a little bit better in life. And he can't really be taken out of the story, both because Thor would never allow it and because, as a god, he's pretty damn hard to kill off. Loki's proven appeal and immense powers means he could honestly be part of every single other Marvel movie going forward. But it's resisting that urge that's going to be the challenge for Marvel for many years to come.

Look only at Jack Sparrow or Mater the tow truck to see what happens when a side character gets too popular and gets exhausted by his franchise. Marvel clearly knows this, and they're bringing in Winter Soldier-- another villain with a personal connection to the hero, it's worth noting-- for the next Captain America movie, and really outdoing themselves hiring James Spader to play a robot for the next Avengers adventure. Spader has been stealing scenes with malevolent charm literally since Hiddleston was born, and stands the best chance of making an actual impact-- that is, if playing a robot doesn't hamstring him the way Dark Elf prosthetics doomed Eccleston. Casting Spader suggests that Marvel realizes they need a new Loki, not just a villain who conveys a threat, but who makes it personal and sympathetic and a little sad. Marvel is banking hard on its heroes for the foreseeable future, but they know they need to bolster their roster of villains too. Loki will be capable of bringing down the house at Comic Con forever… but not if he has to do it every year.