LOS ANGELES (AP) ― Iron Man reigns as the standard-bearer of Hollywood superheroes with a $175.3 million U.S. opening weekend for his latest sequel and an overseas haul of a half-billion dollars in less than two weeks.

According to studio estimates Sunday, “Iron Man 3’’ has raced to a worldwide total of $680.1 million. That includes $175.9 million in its second weekend overseas, where the film has rung up $504.8 million so far.

No other solo superhero ― not even Batman or Spider-Man ― has managed this kind of business.

Yet the future of Marvel Studios’ flagship franchise is in the hands of a mortal man with no metal armor, gadgets or special powers, other than his ability to rebound from Hollywood pariah to hottest star on the planet.

“Iron Man 3’’ hints that Robert Downey Jr.’s Tony Stark might hang up his high-tech suits and live a normal life from now on. As the centerpiece behind not only the “Iron Man’’ films but also Marvel’s superhero ensemble “The Avengers,’’ Downey seems crucial to this comic-book world.

Could Disney’s Marvel Studios conjure anywhere near the same magic if it relaunched “Iron Man’’ with another actor? Without Downey, would the upcoming “Avengers’’ sequel have quite the same appeal as last year’s record-grossing first installment?

“Your guess is as good as mine,’’ said Dave Hollis, head of distribution for Disney. “Marvel has found a way to tell interesting stories with a variety of characters over time, and it will continue to do so.’’

“Iron Man 3’’ had the second-biggest domestic debut ever, behind the $207.4 million start over the same weekend last year for “The Avengers,’’ which teamed Downey’s Stark with other Marvel Comics heroes. The new sequel surpassed the $169.2 million opening for 2011’s “Harry Potter’’ finale, the previous second-place debut.