THE most important people in the fashion industry adore Marc Jacobs.

Alexandra Shulman, editor of British Vogue, for example, describes him as "one of the most talented designers in the world right now. He knows what people want to wear before they do." And you may not know it, but you probably own something inspired by Marc Jacobs. Perhaps it's a subtle nod to the New York designer - the bow on your pumps, the oversize button on your jacket; perhaps it's an out-and-out steal, like the back-alley version of his Jessica Stam bag that you carry. Or perhaps - begging your pardon, madam - yours is the genuine item, a snip at Euro1,136. In a business that is notoriously fickle, what is certain is that Jacobs is a supremely influential fashion designer on top of his game and he's rolling plans for world domination.

Firstly, he's just opened his first UK store, on the site of a former antiques store in Mayfair. He's just closed London Fashion Week with a show unveiling the spring/summer '07 collection for his second line, Marc by Marc Jacobs (which, though you couldn't call it cheap, does not require quite such extensive remortgaging as the premiere Marc Jacobs line).

Irish fashionistas, meanwhile, who have been known to spend inordinate amounts of time in the MJ section in Brown Thomas, are getting very excited about his Waterford Crystal collaboration, which is being launched this month. Now, not only can they tote the bag, wear the clothes (and dress their partner and children in Marc as well), the shades and the scent, but they can also ensure their tables are the best dressed. Marc Jacobs Waterford consists of three patterns of stemware, barware, dinnerware and giftware - Jean, Elizabeth and Robert - called after his closest friends and the embodiment of Jacobs's stylish and savvy design vision. Jacobs says he first became interested in tabletop entertaining and collecting when he moved to Paris to become Louis Vuitton's creative director, and views the Waterford collaboration as "the perfect opportunity to bring my passion for tabletop in the French tradition to consumers worldwide who understand that uncomplicated entertaining does not mean sacrificing elegance and style."

Marc Jacobs was born in New York City in 1963. His father died when he was seven; when his mother, whom he describes as "troubled", remarried five years later, young Marc went to live with his grandmother on Central Park West.

She was a great influence on Marc. "She had very specific shops where she would buy different things, her scarves and her stockings, her coats and capes. . ." he remembers. She also believed in him. In the butcher's, she would tell the staff he was going to be the next Calvin Klein. He followed a time-honoured route: parttime job in a chic boutique, Charivari, and a degree in womenswear at Parsons School of Design in NYC. There, he won prizes: two designer-sponsored Golden Thimbles no less. He designed and knitted his own line in jumpers, decorated with cartoon figures. He started living with his boyfriend and visiting Studio 54 at weekends, not to be seen so much as to see. "I was a voyeur. . . The tall lanky boys in shrunken jackets and girls with leopard-skin eyes - to me, they looked like images from Alice in Wonderland."

He left college in 1984 and hooked up with his business partner, Robert Duffy.

Among Jacobs's gifts is the ability to pick and keep a great team. Venetia Scott, who works with him, is rated by many as the best stylist in the business, a behind-the-scenes star; ditto Suzanne Deakin.

In 1989, Duffy and Jacobs joined Perry Ellis as president and vice- president of womenswear. It was to be a short tenure.

Jacobs proved himself far too edgy for the label, producing a now legendary collection themed around grunge in 1992.

Big mistake. New York was so not ready for satin Birkenstocks, heavy boots and the waif-gone-mad-in-Oxfam look. When Jacobs posed naked between chrome yellow sheets for Vanity Fair, Perry Ellis decided enough was enough and publicly sacked him and Duffy. Jacobs had hired a then little-known denim designer called Tom Ford, and he followed them out of the door too.

It has been said that Jacobs has had "more comebacks than Jamie Lee Curtis in Freaky Friday", and this was his first. Duffy sold his house to meet their bills (Jacobs didn't have one to sell).

Jacobs set up his solo label. Donatella Versace and Anna Wintour joined in the standing ovation for his first show. He became New York's "dauphin of grungy, understated cool" (US Vogue). There followed a spell in rehab, which left him teetotal. "I can't go back there, not for a second."

He lives quietly in Paris now, where he enjoys shopping for silverware and walking his dogs. But the man still loves a party. His label's Christmas do is always an event. Last year its fancy dress theme was Venetian Carnival, and Jacobs, mindful of the occupants of St Mark's Square, went as a pigeon.

Suzy Menkes has observed that in fashion, nowadays, individual designers have no power without mega-companies behind them. This was true for Marc Jacobs, and it was only when he was hired by Louis Vuitton in 1997 that he and his solo label gained real heft. "They were kind of our saviour, " he says, of LVMH - though that accolade could also go to Winona Ryder, who liked his clothing so much she stole several items from Saks.

At LVMH, things did not go entirely smoothly, however. He did away with the LV monogram and produced - brace yourself - a plain Vuitton bag. Then he engaged the Japanese artist Takashi Murakami to doodle on a clutch bag, and NY veteran Stephen Sprouse to graffiti a slouch. But when these designs became so popular that the revenue of LVMH doubled, Jacobs was vindicated.

With characteristic prescience, he had foreseen that the public mood was turning against ostentatious labelling. He picked up the fin-de-siA"cle vintage trend early, too.

Jacobs's approach is not pretentious or esoteric.

"I know a piece will work when I can imagine someone I know running around in it, " he says. But before we get too carried away and call him a designer with a common touch, let us remember that chum of his he is imagining running around is probably Debbie Harry or Sofia Coppola.

He has friends in vertiginously high places: Chloe Sevigny, Liv Tyler, Daryl Hannah, Jarvis Cocker, Hilary Swank - the list goes on. But unlike, say, Giorgio Armani, he never gives the impression of haughtiness. The advert for his perfume, for example, was an out-of-focus poolside snap of Sofia Coppola, a statement of his laidback, intimate aesthetic.

His casual look, though, comes at a price.

One of the most expensive handbags in Brown Thomas, for example, is his Dentille Bag, which sells for Euro1,000. A recent Vogue article laid the blame for our current mania for expensive handbags at his door. Yet despite the hyper-inflated prices, the ubiquitous high-street copies and the everexpanding empire (stores area also opening this spring in Tokyo, Dubai and Savannah, Georgia) Jacobs remains a likeable figure, a modest, non-showy fashion designer who acknowledges his success cannot but fade.

"I'd like it to go on for ever, though, " he says, with a smile.

'Marc Jacobs Waterford' is available exclusively in Brown Thomas