Iron Man reigns as the standard-bearer of superheroes with a $175.3 million domestic opening weekend for his latest sequel and an overseas haul of a half-billion dollars in less than two weeks.

According to studio estimates on Sunday 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.

No other solo superhero – not even Batman or Spider-Man – has managed this kind of business. But the cloud on the horizon is whether actor Robert Downey Jr. will continue as the face of the franchise.

Celebration: Actor Robert Downey Jr. and his Iron Man character rang the opening bell ceremonies of the New York Stock Exchange at the end of April. They will be now be celebrating a record-breaking opening weekend

The new Iron Man sequel surpassed the $169.2 million opening for 2011’s Harry Potter finale, the previous second-place debut.

The movie 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.

In just nine days, the film shot past the $312 million international total for Iron Man 2 in its entire theatrical run.

Among the overseas totals so far: $63.5 million in China, $42.6 million in South Korea, $38.3 million in Great Britain and $35.8 million in Mexico.

Domestically, Iron Man 3 far outpaced the franchise’s first two movies. Iron Man launched the series with a $98.6 million domestic debut in 2008, while 2010’s Iron Man 2 opened with $128.1 million.

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.

Success: Iron Man 3 seen here with girlfriend Pepper Potts played by Gwyneth Paltrow achieved the second-biggest domestic debut ever with an astounding $175 million

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 flicks 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.’

If Downey doesn’t sign on for more, it would leave a gaping hole in the expanding superhero universe Marvel is taking to the big-screen.

Face of a franchise: 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. Could he be replaced?

‘I honestly don’t know how you can go on with that character without Downey,’ said Paul Dergarabedian, an analyst with box-office tracker Hollywood.com.

‘I think he’s as important to this franchise and to Marvel as any actor is to any character.’

Downey seems just as vital to The Avengers.

That ensemble probably could thrive without him, given how the first film and previous solo superhero adventures have established a team that includes Chris Hemsworth’s Thor, Chris Evans’ Captain America, Scarlett Johansson’s Black Widow and Mark Ruffalo’s Hulk.

But without Downey, Marvel might have to settle for something less than the colossal $1.5 billion worldwide results for The Avengers.

‘He’s the spark that ignites all those characters, it seems,’ Dergarabedian said. ‘He’s the lead guitarist, and they’re just all kind of following him.’

Before convincing reluctant Marvel executives that he was the man to put on the metal suit, Downey still was trying to live down drug addiction and jail time in his 20s and 30s that nearly ruined his career.

Dynamic duo: Downey said that Avengers director Joss Whedon told him the movie didn’t really start until his character and girlfriend Pepper Potts (played by Gwyneth Paltrow, pictured) appeared together on screen

The success of Iron Man led to another blockbuster franchise in Sherlock Holmes, and Downey’s professional choices now look limitless.

In an interview before the release of Iron Man 3, Downey said that Avengers director Joss Whedon had been editing a first cut of that film and told him the movie didn’t really start until Stark and girlfriend Pepper Potts (Gwyneth Paltrow) appeared together on screen.

Downey said that was a testament to the groundwork laid years earlier in Iron Man, which ‘when we were shooting it, this kind of became the heart of several franchises.’

‘So you know we’re having a nice time,’ Downey said, sidestepping comment on whether he might return for more Iron Man and Avengers sequels.