Only one person can make or break a potential blockbuster before it hits theaters, and he doesn't work in Hollywood or control a penny of the multi-million-dollar budget. He lives in his parents' basement and sometimes wears a capebut the much-mocked comic-book geek possesses the ass studio execs must kiss to hit superhero-movie gold. Thanks to favorable early buzz, Iron Man and The Dark Knight banked more than $575 million and more than $990 million, respectively, making them the top-grossing films of 2008. It's no coincidence the producers and casts of these smash hits made the same pit stop on the road to box-office dominance: the Comic-Con International festival in San Diego, where they schmoozed the nerdy throngs, sat on panels, debuted Joker-laden teaser trailers, and forced Robert Downey Jr. to smile and wave like a homecoming queen. There's a reason that Zack Snyder, director of 300 and next year's Watchmen, says each of these rabid conventiongoers is "worth 20 normal fans." He knows the death knell of the next megabudget superhero flick will sound curiously like The Simpsons' Comic Book Guy: "Worst. Movie. Ever."