Jennifer Lopez: She can sing, she can act, she knows how to behave. Badly

Yes she has the tantrums, the vast entourage and the messy private life. She's the very picture of an A-list celebrity. But she can also out-sell Kylie and out-act Madonna

Was there ever a time before J-Lo? Like Michael Jackson, Whitney Houston and Madonna, Jennifer Lopez seems to have been a fixture in the celebrity firmament forever: an endless stream of dull-gold split-to-crotch gowns and surprise-choice boyfriends. Yet the singer-actress soared to fame a mere four years ago. She's at that level of fame that means her marriage to an obscure dancer still makes headlines on the eve of war and Donatella Versace insists on a piece of the wedding action.

The multi-tasking Ms Lopez is now making entertainment history of a thoroughly modern kind. She is the only actress and singer ever to have made her début simultaneously in the top spot of the movie and music charts. In an era when style outperforms substance pretty much everywhere, she manages both to overachieve and to swan through that thin-air world of celebrity where plunging necklines gain more column inches than hit movies. The level of gossip, paparazzi fervour and speculation-cum-adoration that she inspires is more commonly reserved for the seriously weird. Yet her career credentials outdo most A-list celebrities to the power of two, and leave Liz Hurley gasping for air. She is also the only Latina actress ever to earn a film salary of more than $1m. "There is one person on this planet whom I'm in competition with: myself," she says.

Lopez was born to Puerto Rican parents in the Bronx, New York, in July 1970, the daughter of David, a computer programmer, and Guadalupe, a kindergarten teacher. The fledgling star nurtured big dreams, in true 20th-century American style. She started singing and dancing lessons at the age of five, danced in local productions of Oklahoma and Jesus Christ, Superstar, and toured Europe and Japan with stage musicals.

It was in 1990, as a "Fly Girl" dancer on Fox's In Living Color, that she received public recognition, to be followed by further small screen roles. There is dross, of course, deleted from the CV. In Lopez's case, history barely recalls her 1993 role as Rosie the nurse in Nurses on the Line: The Crash of Flight 7. It was followed in 1995, however, by the more critically acclaimed Mi Familia, the story of Mexican immigrants in Los Angeles.

But the Jennifer Lopez so firmly – however sketchily – lodged in our consciousness was born in 1997, when she won a nation-wide search for the lead role in Selena, Gregory Nava's film about the murdered singer, and was subsequently nominated for a Golden Globe award. Ojani Noa, a Cuban waiter, publicly proposed to Lopez at the wrap party for Selena. The marriage – her first, although there are rumours of a predecessor – lasted a year.

Once propelled into the A-list (Out of Sight with George Clooney clinched the demarcation), the roller-coaster ride between the serious and the salacious began to roll. "It was my time to shine," she said. Even when her hit film The Wedding Planner and multi-platinum album J-Lo claimed joint chart victory, who had seen more than one Lopez movie or could hum a Lopez single? No, what we vaguely know about J-Lo is the trivia: the silly moniker, the famed rear, the Puff Daddy period, the star's requirements, and the plunging necklines. And now the nuptials to Cris Judd, 32. The dancer accompanied her to the Academy Awards a mere month after her split from Puff Daddy. His current claim to fame is, frankly, his marriage to Lopez. Shades of Carlos Leon, fitness instructor and father of Madonna's first child. The Lopez-Judd wedding was followed by a celebratory dinner thrown by Donatella Versace at her villa beside Lake Como, where minor stars mingled with journalists who had never even met the happy couple before finding themselves on the invitation list.

Rather than the cool, mellow tones one might expect from la Lopez, her voice is somewhat thin, her sound reliant on electronic backing, and there are even rumours that she doesn't sing all her material herself. She was recently tainted with controversy again when she made a "nigger" reference in her single "I'm Real", for which she was booed on-stage and branded "common Bronx trash" in the black-American press.

J-Lo has the fame thing covered. The navel-revealing little number that she wore for the Grammies was so photographed that it acquired "that dress" status. In quick succession she was named one of People magazine's "50 most beautiful", released her first multi-platinum-selling album, and was detained with the rapper Puff Daddy, her then boyfriend, in connection with a nightclub shooting.

The relationship with Puff Daddy was volatile. "We were like panthers in a cage," she commented. He stood trial for gun possession and bribery offences. The column inches around the couple proliferated.

Lopez, who had thus far alternated between hard-working good girl and standard sex siren, acquired some tougher bad-girl credentials, mixing the worlds of glamour and the mean streets. She split up with a devastated Puff Daddy, reportedly on Valentine's Day, but not before he had sent her 100 white doves. The superachiever was back in place, starring in The Cell, and dominating Hollywood.

The transition from singer to actor is notoriously treacherous, a feat even Madonna has spectacularly failed to pull off. Most unusually, Lopez did it well, and did it the other way round. "I'm like a juggling act," she says.

Her first album was named On the 6, a reference to the subway train that links Manhattan and the Bronx. The J-Lo homegirl vibe is strong, calculated and polished to perfection. While reportedly given to tantrum-throwing demands, vast entourages and fastidious dietary requirements, she retains a strong and knowing streak of the Bronx beauty parlour. Her fans are mostly teenage girls, who can probably just emulate the tamer of her looks from the local shopping mall. As a child she was known locally as the Supernova. At 18 she set off for Manhattan, determined to further her fame plans: "I have this thing inside me that tells me I'm going to do this or die trying."

The rags-to-riches tale is part of her almost scarily effective global appeal. Now beginning to supersede Madonna as the US's most prolific cultural export, she is the catch-all superstar who has enacted the American dream. Her role as Hollywood's leading Latina lady somehow sidesteps both politics and clearly defined race issues. She is the all-American light-skinned Latina with the looks of an airbrushed cyber-heroine: golden, honeyed, not black or white but in-between and changeable. She is slippery, hard to define in a way that makes Madonna look crass and dated.

With her tawny highlights and perfectly regular features, she manages to look devout even as she smoulders. "I want it all," she has said, and indeed, she does seem to have it. She may be notorious for her awards-ceremony appearances and video performances in which tits-and-ass predominate, but her expression remains impassive: soft, intimate, almost withdrawn, beneath her Fifties air-hostess coiffure. She possesses a bottom so famed that she is said to have insured it for $1bn, a notion she dismisses. "I could serve coffee using my rear as a ledge," she says.

Where others in the business re-design themselves, she merely tweaks the original. Her latest project, a clothing line, is named Sweetface. The face may be sweet, the temperament isn't always.

"It was like something out of a spoof," says a BBC source of J-Lo's famed visit to the Top of the Pops studios. According to reports, she commandeered 10 dressing-rooms, had them re-designed, and brought an entourage of 60, including three chefs. The mixture of savvy careerist and chaotic homegirl-made-good is apparently irresistible

"I think I' m normal, and a lot of people ain't normal in this business," she says. That's normal as in Supernova-normal.