Fame in 2012 has a unique set of parameters. The boy band One Direction have ticked off all the traditional markers of global success – a debut single that topped the UK charts, a debut album that topped the US Billboard charts, hordes of fans swarming over them at every public appearance, tabloids peppered with stories of bad-boy behaviour.
But they've also attracted those quirks of celebrity culture that solidify their status as a phenomenon. There are slash-fiction blogs dedicated to imagining romantic relationships between the band's five members. Their blazers and chinos have had an impact on menswear sales. You can buy hair straighteners with the 1D logo. There are dolls. There is mania.
In short, Harry Styles, Louis Tomlinson, Niall Horan, Zayn Malik and Liam Payne are very, very famous, and very, very successful. It's hard to remember them as they were in the early stages of The X Factor, in the summer of 2010, all singing for a shot at solo stardom, before Nicole Scherzinger smooshed them together as a band.
Watching their try-outs again on YouTube is a reminder of how far they've come. Malik is so nervous about a dance routine that Simon Cowell has to give him a pep talk. Horan barely scrapes through his initial audition. Only Styles has the confidence of someone who knows they've got the full package, and at that point he's still only 16.
By the time they got to the studio shows, it had begun to fall into place.
"For me, their future global success was cemented as soon as they performed Kelly Clarkson's 'My Life Would Suck Without You' on the second live show," recalls Peter Robinson, who runs the website Popjustice.
"They looked perfect. Their vocals were all over the place, of course, but that wasn't the point."
They didn't win The X Factor in 2010, coming third, behind Rebecca Ferguson and the series winner Matt Cardle. It was a surprising result.
Every weekend, while the show was being filmed, the TV studio in Wembley would be overrun by fans holding homemade banners, pleading with employees to pass on adoring messages to the boys. But losing did them no harm; on the contrary, it released them from the so-called "winner's curse".
Cowell signed them to his label, Syco, anyway. They had used the 12 weeks of the show to carve out a niche – their ease with Clarkson's pop-rock hit foreshadowed the broadly appealing sound they'd take to the top.
There was a moment during the final, when, after Cardle had been crowned triumphant, Styles whispered something rude into his ear, forgetting that millions of viewers would find it easy to lip-read. It was crude, but it firmly established his image as a cheeky, up-for-it lad.
After The X Factor, and the show's subsequent annual arena tour, One Direction were packed off to work on their debut album.
Its first single, 'What Makes You Beautiful', came out in September 2011, breaking pre-order records for Sony. It blends upbeat pop-rock with blandly supportive, nice-guy lyrics, though older listeners may find its platitudes patronising. It won a Brit award for best single in February.
Next on the to-do list was North America, where they spent months on the TV and radio circuit. I spent some time in Texas in April, and it was impossible to flick on a radio station without hearing a guest-jingle recorded by the boys. They were everywhere before their music was everywhere.
When their album was released, it went straight to No 1, a feat no "British" boy band, from the Beatles to Take That, had managed to pull off before. A second album, Take Me Home, was released last week, and will be carried to inevitable success by lead single 'Live While We're Young'.
Their laddy persona has been an important part of why it works. It covers all corners. It means that mums can claim them as a guilt-free pleasure, and daughters can swoon over them as potential mates (it is no coincidence that the "nice" one, Niall Horan, has sold the most dolls in his likeness).
Even hard-to-please fashionistas have got on board – the band are on the cover of the Christmas issue of style mag Wonderland, and Grazia magazine sent a writer to east London clubs in pursuit of Styles on a night out.
In his recent New Yorker profile of the band, the critic Sasha Frere-Jones said that "lads are now in boy bands, and they need not dance".
I asked him to expand on what he meant. "For me, it's cynically setting up a target demographic," he explains. "Eight-year-olds don't buy anything. Their moms buy it for them. So if you can get that teenage audience, who have control of their own money, to like it too, you'll have a longer career."
A subtle suggestion of bad behaviour, he says, is part of the package. The single 'Up All Night' includes lines like "People going all the way, yeah all the way / I'm still wide awake" and "I wanna stay up all night /And do it all with you".
"'Let's get drunk and f**k' is in there, coded," says Frere-Jones. "It's clever and calculated. They're saying they're not completely clean-cut. Why do you think they're up all night?"
Some critics complain that while they have the looks and the moves, they don't have the tunes, but Peter Robinson disagrees.
"Syco's careful calculations have paid off for One Direction," he argues, "but Syco carefully calculate everything they do, with mixed results. It was theirs to mess up, really, and as soon as I heard their debut single I knew they'd got it right."
It is also a matter of timing. The audience was ready for it. One Direction are far from the stagnant anthemising of Westlife. Take That are no longer for the kids. Every generation needs a boy band, and One Direction fit the bill. The question is whether they can sustain it.
"There's great power in inertia. They'll sell a lot of records for a long time, even if it's garbage. They could issue tax returns right now and still sell a million copies. Buzz sustains them," says Frere-Jones.
As for the solo career that usually tears an ensemble apart – see the Spice Girls – it may not be a concern. At this stage, it takes the five of them to keep this machine ticking over.
And that may come as a relief to writers of slashfiction, sellers of chinos and self-loathing, curly-haired girls everywhere.