The many faces of Beyoncé

Tonight's headline act at Glastonbury captivates and puzzles at the same time

I'm in an electrical shop in a small market town in Suffolk, about to leave, when I see them busting out of the flat-screen display tellies. Thighs. They're not skinny model ones but rather a muscled, powerhouse pair; oak trees that contain erupting volcanoes, kick-you-out-of-the-house-in-one-thrust sort of thighs. And she's shaking them, and her arms too, and her arse is all of a turbo shimmy, South African tribal dance style.

She's live in concert somewhere and I'm stuck in the shop for a good 20 minutes just gawping, convinced that even the cheapest TV set has now become 3D. They haven't put the sound on so I can't even hear the singing, which is just as startling as her limb control, with R'n'B choruses as catchy as pig flu. Or appreciate the pop lyrics, which are all about females and their big juicy strength; making their own money, experiencing their own love, their fortitude.

It is clear, solely from that Joan of Arc look of destiny in her eyes, that this isn't girl power. This is woman power. This is Beyoncé. So some years later it makes perfect sense that the 29-year-old is headlining this weekend's Glastonbury festival and expected to attract a huge audience on the BBC's coverage of the event tonight.

After her early years in the teenage girl band Destiny's Child, Beyoncé Knowles has ascended to become the greatest solo pop star of the millennium. Forget Lady Gaga, with her tinny songs and her victim rhetoric that can seem so contrived, so pouty and whiny. Beyoncé doesn't need to get attention by pretending she has a penis or by wearing meat – Beyoncé has balls of her own. Beyoncé is the meat.

She's a self-described feminist, a businesswoman and, since her marriage to hip-hop mogul Jay-Z, one half of what Forbes magazine describes as "the most powerful couple in entertainment". Indeed, Queen B herself says that if she hadn't been there with her husband when he headlined Glastonbury in 2008 – a controversial event, because he's a rapper – she wouldn't have done it herself this time. Yet no such controversy has erupted over her name going on the programme. Everybody, even your granny dancing at a wedding, loves a bit of Beyoncé. But does everybody really have a clue who she is?

Compared with those "private" couples who seem to do an awful lot for the cameras, Jay and Bey's relationship really is an enigma. And though Beyoncé performed at Obama's inauguration, she had done the same for George Bush. Often voted the sexiest woman in the world, with that gravity-defying booty, Beyoncé had a huge hit celebrating all the single ladies – yet she's also a Texan Methodist who hints that her husband is the only man she's ever been with.

Her critics say she has trampled and pushed to get where she is; her friends say she is a sweet girl who works incredibly hard. It seems Ms Knowles has several faces. Would the real Beyoncé please throw her hands up?

Beyoncé: The pop star

You know the story – overbearing parent turns their child into a star; the kid gets a record contract at age 12 and ends up wondering where it all went wrong. Except that for Beyoncé, whose dad was indeed the pushy manager of her teenage girl band Destiny's Child, it all went right.

Somehow, Beyoncé managed to quit the band and her father's clutches, and become even more successful. (In fact, she recorded her first solo album, with its smash hit "Crazy in Love", in secret in two weeks.)

What she did next was a little bit extraordinary – she took the women-friendly themes of Destiny's Child and amplified them. Beyoncé's solo lyrics are about how a diva is a female version of a hustler, about what she would do if she were a boy, about how girls run the world. Female musicians play on tour with her. So it's a feminist revolution, right?

Well, perhaps inevitably, with this kind of drive come sacrifices. At the recent Billboard awards, B made a very humble speech in which she paid homage to the original members of Destiny's Child, including LeToya Luckett. Yet Luckett told me sadly that if she could write just one last letter in her life it would be to Beyoncé, to tell her how it felt when she was pushed out of the band. All of this only makes the rumour that Destiny's Child may be on the Glastonbury stage tonight all the more exciting. In any case, remember when Beyoncé came on to The X Factor to sing with Alexandra Burke, who could only tremble? A runner from the show says they watched Beyoncé spend hours helping Burke rehearse, being utterly lovely the entire time.

Beyoncé: The mogul

It's no coincidence that B is playing Glastonbury the day before her new album, 4, launches. She recently said that she falls asleep with her hand still on her BlackBerry, "sending emails, coming up with marketing plans and looking at radio numbers". Her licensing deals aren't quite as omnipresent as some stars', but she still does well out of the multiple platform brand thing – perfume, a fashion line, the L'Oréal ads in which she looks strangely white. Forbes magazine has estimated her earnings at between $30m and $85m a year, depending on whether she releases an album. Clearly, she follows a similar philosophy to her husband, who wrote in his book Decoded about how dealing drugs on the street taught him how to hustle in hip-hop and make his millions. "In business, like they say, you don't get what you deserve, you get what you negotiate," he wrote. "So I mind my business and I don't apologize for it."

Perhaps this explains why she accepted a cool couple of million to play a private show for one of Gaddafi's profligate sons. She has since said that she gave the money to charity, but it still seems odd that somebody so keen on liberation would play for a regime so repressive. Indeed, the video for her latest single, "Girls (Run the World)", shows an army of wild, freedom-fighting women overpowering military men in a desert. (She sourced the dancers from Mozambique.) It seems she borrowed the dance from them and borrowed the imagery from a South African photographer.

The video shows her as a rebel, posing with animals, weapons, practically fangs. All of the women have wild, free hair, not straightened. And yet she is a capitalist superpower. The age of pragmatism, winning out over all other isms, has worked well for Beyoncé. Even her friendship with the Obamas doesn't necessarily make her a Democrat, just pro him. But it would be nice, one day, to see her nail some colours to some mast somewhere.

Beyoncé: The wife

Rather astonishingly, Beyoncé has said on more than one occasion that Jay-Z was her first proper boyfriend, after a long teenage affair with another guy in which "we didn't live together, we didn't, you know...". Which means – OMG!! – that she has probably been to bed with only one man. Which makes all her love songs and break-up songs and sex songs all the more confusing.

She also says she wants a bunch of kids but then gets vague, and says you can't plan these things. Obviously we don't believe this for a second, since she looks like somebody who could train her ovaries to sync with the stopwatch on her husband's Rolex if she so wanted to – which she wouldn't – but still.

Their marriage is a thing of wonder to us mere mortals. Do they sit around shouting at the telly together? Doing Sudoku? Having brunch with their unlikely best friends Gwyneth Paltrow and Chris Martin? (When Gwyneth asked Jay-Z, on her website Goop, how he got to be the coolest man in the world, he said it was because of the amazing women he has surrounded himself with, such as his mother and his wife.) Or do they just have hours of mindless, we-are-two-of-the-very-most-amazing-people-in-the-world sex.

Well done Jay-Z, however it was you did it, since no details or pictures of your secret wedding in 2008 have ever come to light. We can only assume that you did indeed put a ring on it.