Then Downey took the mic, with full Tony Stark swagger.

“Anybody see Inception?” Downey asked. “I think that was probably just about the most ambitious movie I’ve ever seen. And then I thought, ‘Wait a goddamn second. Marvel Studios is going to take all of their top superheroes and they’re gonna put them all together in The Avengers? That’s the most ambitious movie I’ve ever seen.”

Downey introduced Ruffalo, demanding that fans welcome the actor into the role formerly played by Edward Norton.

It was the kind of revelation that confirms Comic-Con’s Hall H as ground zero for genre film announcements, with studio panels becoming increasingly like Apple’s patented product reveals. Marvel Studios President Kevin Feige even ripped off Steve Jobs’ “one more thing” bit, tacking on the Avengers casting news and curtain call after showing footage of Thor and Captain America.

After the Ruffalo casting news, Downey called onstage Joss Whedon, the director who confirmed his own participation in The Avengers previously at this year’s Comic-Con during a brainy head-to-head with J.J. Abrams.

“I had a dream,” said the typically self-deprecating Whedon, “and it was not this cool. I want to thank Kevin [Feige] so much, for bringing me on, for trusting me, and assembling my dream team. This is the Avengers,” he said referring to the actors on the stage.

“A team is more than the sum of its parts,” Whedon continued, “this cast is more than I could ever have dreamed for. And I am going to blow it!”

Photo: The Avengers cast and filmmakers assemble at Comic-Con International 2010 in San Diego. From left, actors Robert Downey Jr., Clark Gregg, Scarlett Johansson, Chris Hemsworth, Chris Evans, Samuel L. Jackson, Jeremy Renner, Mark Ruffalo, director Joss Whedon, producer and Marvel Studios President Kevin Feige. Photo courtesy Marvel Entertainment.