Banksy: the star without a face.
Virtually no one knows who the artist Banksy really is. But his work is selling for five-figure sums. Rebecca Rose reports.

Nearly 15 years ago, when stencilled images by graffiti artist Banksy started to pop up overnight on walls, bridges and other public spaces across UK cities, they were hastily painted over or scrubbed off by local authorities and disgruntled residents. Now those in possession of a blank wall may well be crossing their fingers that this most invisible - yet celebrated - street artist, known for his subversive designs and comments, will pay them a visit in the wee hours. This is not representative of a general swing in attitude towards graffiti but is specific to the popular thirtysomething Bristolian spray-painter, who has become the contemporary art market's darling of the year - a "Banksy" on the side of your house may well increase the value of your property.

Three years ago, Bonhams was the first to dare to sell a Banksy at auction; it fetched £580. On October 25 this year, Bonhams sold one on behalf of an anonymous vendor for more than 100 times that amount - a spray-on-steel work of an embracing couple wearing divers' helmets that was a design for Blur's Think Tank album cover. The work, estimated at £5,000-£7,000, went for £62,400 to a UK collector. The sale hit headlines everywhere; now the chunky lettering of the artist's sprayed name tag - once iconic to teenage graffiti-heads only - has officially become a sought-after brand in UK contemporary art circles. And owners of works by Banksy - often people who bought from the artist himself for only a few hundred pounds - are keen to seize the moment to sell. "The sale was packed out," says Bonhams' Emma Cork. "It was attended mainly by young wealthy media types under 40."

In terms of the art world and media interest, this has been Banksy's year. A few days before the Bonhams sale, Sotheby's had its own Banksy moment. On October 19 the company's Olympia saleroom sold an early example of the artist's "vandalised oils" - a copy of the "Mona Lisa" customised by Banksy to show her eyes striped with paint (estimated at £15,000-£20,000), which went for £57,600 to a private US collector. Sotheby's also sold Banksy's updated Warholesque Marilyn Monroe screenprints (Kate Moss is the new Marilyn here) for £50,400 - more than five times the estimate. This was Sotheby's third sale of works by Banksy this year.

The artist, however, was not present at any of his sales. As far as anyone knows, that is. Neither Bonhams nor Sotheby's have actually met or spoken to him - all dealings have been via his agent of five years, Steve Lazarides. While Banksy's name proliferates in the press almost nobody knows who he is.

This anonymity is a hangover from his early days tagging in Bristol when remaining incognito was the only way to avoid arrest. Nowadays it serves a dual purpose. Banksy - whose real name might be Robert Banks or even his cheeky nom de plume Robin Banksy - may be increasingly friendly with the hammer of Bond Street but he is still a graffiti pest who regularly adorns public property. In addition to his urban al fresco work, which has made him widely known throughout the UK for more than a decade, he is also known for his political pranks. These range from sneaking a blow-up doll dressed as a Guantanamo Bay inmate (orange outfit, black hood) into Disneyland to spray-painting idyllic imaginary windows and escape routes on to the Palestinian side of the West Bank separation barrier.

He has also put two fingers up to the art establishment by smuggling his work into major UK and US galleries. His hoax cave painting, which showed a primitive man pushing a shopping trolley, lasted two days in the British Museum before it was discovered; it is now part of the permanent collection. "They are good enough to be in there - so I don't see why I should wait," he commented.

Banksy's stunts are not only for fun, or to make a point, they are also a maverick form of marketing, assuring maximum media coverage and public excitement. His anonymity plays an essential part in heightening the sense of mystery around his increasing omnipresence. Just before the October sales, Banksy whipped the LA art scene into a frenzy by casually announcing on his website that he was to hold a three-day exhibition in an LA warehouse, entitled Barely Legal. The opening night was surprisingly star-encrusted; Brad Pitt and Angelina Jolie reportedly spent £200,000. The show consisted of 50 works and included the controversial figure of a real elephant, painted in gold and red to blend in with the wallpaper behind - a live representation of the proverbial elephant in the room. While the event seemed spontaneous it has been revealed that the show had been planned for six months.

Some pre-show pranks in both LA and the UK made sure he was suitably in the public eye at the time too, notably his extraordinary act of obtaining 500 CDs of Paris Hilton's new album, superimposing a dog's head on top of the socialite's cover photo, attaching stickers boasting tracks such as "Why am I famous?" and a bogus bonus track and sneaking the CDs back into the shops. Unsurprisingly, they became highly sought after, fetching £750 on Ebay.

It seems that, by his wrongdoings, Banksy can do no wrong. This should ensure that the value of his works continues to escalate - to the delight of Banksy owners. But with unauthorised Banksy stencil kits for sale on the internet and his unwillingness to reveal his identity (even his mother and father apparently think he is a painter and decorator), surely it is tough for dealers and auction houses to know a real Banksy when they see one? Chairman of contemporary art at Sotheby's, Cheyenne Westphal, explains that this is not the case: Banksy's dealer, Lazarides, authenticates all real Banksys with a thumb-printed certificate. Whether it is Banksy's own smudge or not, Westphal doesn't know. This is Banksy and Lazarides' attempt to keep his commercial art (mainly stencil-on-canvas work and vandalised oils) separate from his street art, which they wish to remain free for all.

It is inevitable, however, that the more everyone wants a piece of Banksy, the more early known examples of his street art will have a market value. Two such works, one of two policemen running (an iconic Banksy motif) and another small stencil of a leopard - both of which come from the side of a Bristol pleasure boat that has since been dismantled - are up for sale next April at Bonhams. Sotheby's will also have Banksys in their February sale but are sticking to his higher-value, certificated works.

There is no doubt that Banksy's status has shifted. His bestselling book Wall and Piece has sold more than 140,000 copies in the UK alone; it is now out in paperback. While he still keeps one foot in the street - which saves him from selling out in the eyes of the graffiti community - the other is making its mark in the lucrative world of contemporary art. A Banksy is currently on show at the Serpentine Gallery in Damien Hirst's collection, linking him not only with names such as Andy Warhol and Francis Bacon but also with the Britart jetset.

"He really is an exciting artist," says Westphal. "Instead of making some obvious political statement, he does it with poetry and energy and humour." As for his market value, Westphal is equally positive. "My feeling is that we are still at the beginning."

Lazarides agrees "The things that are happening are now are beyond our control," he says. "It wasn't us driving those prices. There are now so many people who want his work - and only a limited amount of it is around."