Since Banksy made his name with his trademark stencil-style 'guerrilla' art in public spaces - on walls in London, Brighton, Bristol and even on the West Bank barrier separating Israelis and Palestinians - his works have sold for hundreds of thousands of pounds.
In the frame: The man in this photograph, taken in Jamaica four years ago, is believed to be Banksy
He is also known for his headline-making stunts, such as leaving an inflatable doll dressed as a Guantanamo prisoner in Disneyland, California, and hanging a version of the Mona Lisa - but with a smiley face - in the Louvre, Paris.
But perhaps his most provocative statement, and the one that generates the most publicity, is the fact that Banksy's true identity has always been a jealously guarded secret, known to only a handful of trusted friends.
A network of myths has grown up around him. That his real name is Robin Banks. That he used to be a butcher. That his parents don't know what he does, believing him to be an unusually successful painter and decorator.
Then there's the suggestion that Banksy is actually a collective of artists and doesn't exist at all.
Such is the curiosity about Banksy that when the great man threw a pizza box into a bin in Los Angeles, the box resurfaced on auction site eBay, with the seller suggesting that the few anchovies left inside might yield traces of his DNA.
He is the Scarlet Pimpernel of modern art, so adept at leaving false trails that even his own agent has claimed that he is not certain of his identity.
Indeed, trying to establish just who the elusive Banksy is has proved as difficult as predicting the location of his next work.
But now, after an exhaustive year-long investigation in which we have spoken to dozens of friends, former colleagues, enemies, flatmates and members of Banksy's close family, The Mail on Sunday has come as close as anyone possibly can to revealing his identity.
And far from being a radical tearaway from an inner-city council estate, the man we have identified as Banksy is, perhaps all too predictably, a former public schoolboy brought up in middle-class suburbia.
Our search began with a photograph taken in Jamaica showing a man in a blue shirt and jeans, with a hint of a smile on his face and a spray can at his feet.
Taken four years ago, it was said to show Banksy at work. When the picture was published it appeared to be the first chink in the armour of anonymity with which the artist has shielded himself ever since his work began to attract the attention of the art world.
Naturally, Banksy denied the picture was of him. Indeed, as we discovered, Banksy and those close to him tend to deny everything.
Armed with this photograph, we travelled to Bristol, long said to have been Banksy's home city, where we made contact with a man who claimed to have once met the artist in the flesh.
Of course, many people claim as much, but the moment one starts asking for more information, one discovers they actually 'know someone who met Banksy' - and the trail runs cold.
However, this man claimed not only to have met the elusive artist but was able to furnish us with a name - not the usual variations of the name Banks but one all the more intriguing.
The man in the photograph, he insisted, was formerly known as Robin Gunningham - and it didn't require much imagination to work out how such a name could result in the nickname Banksy.
From records available to the public, we were able to glean further information.
Mystery boy: Robin Gunningham in 1989 when he was a pupil at Bristol Cathedral School, below
Robin's father, Peter Gordon Gunningham, 66, is a retired contracts manager from the Whitehall area of Bristol. His mother, Pamela Ann Dawkin-Jones, 67, was a company director's secretary and grew up in the exclusive surroundings of Clifton. She now works in a nursing home.
The couple married on April 25, 1970, at Kingswood Wesley Methodist Church. On February 8, 1972, their daughter Sarah was born at Bristol Maternity Hospital, by which time Peter had been promoted to area manager for a hotel company and the couple had bought their first home, a semidetached house in Bristol.
On July 28, 1973, Robin was born in the same hospital. According to neighbours, the boy had early surgery for a cleft palette.
When Robin was nine, the family moved to a larger home in the same street and it is there he spent his formative years and became interested in graffiti.
A neighbour, Anthony Hallett, recalls the couple moving into the street as newlyweds and living there until 1998. They have since separated.
When we showed Mr Hallett the Jamaica photograph, he said the man in it was Robin Gunningham.
In 1984, Robin, then 11, donned a black blazer, grey trousers and striped tie to attend the renowned Bristol Cathedral School, which currently charges fees of £9,240 a year and lists supermodel Sophie Anderton as a former pupil.
It is hard to imagine Banksy, the anti-authoritarian renegade, as a public schoolboy wandering around the 17th Century former monastery, with its upper and lower quadrangles and its prayers in the ancient cathedral.
But we then found a school photograph, taken in 1989, of a bespectacled Robin Gunningham in which he shows a discernible resemblance to the man in the Jamaica photograph.
Indeed, fellow pupils remember Robin, who was in Deans House, as being a particularly gifted artist.
Scott Nurse, an insurance broker who was in Robin's class, said: 'He was one of three people in my year who were extremely talented at art. He did lots of illustrations. I am not at all surprised if he is Banksy. He was also in the house rugby team and I think he played hockey as well.'
In the rare interviews Banksy has given (always anonymously), the artist has acknowledged that it was while at school that he first became interested in graffiti.
Banksy's sandwich board-wearing monkey sold for £228,000 this year. He has also painted murals including a Mona Lisa with a rocket launcher
In 1983, the New York hip-hop group the Rock Steady Crew toured Europe, appearing at the Royal Variety Performance with a number of graffiti artists. This performance was the inspiration for artists such as Massive Attack's 3D and Nick Walker, now an equally high-profile artist and designer who did the backdrop for the films Eyes Wide Shut and Judge Dredd.
But Banksy's interest in the art is said to have caused a family rift.
Former neighbour Mr Hallett said: 'The family was always very nice. I don't know for sure but I think Robin was working as a graffiti artist. He worked for other people and would disappear for months on end. He was quite nomadic.
'I would not go as far as to say he went off the rails, but there was some sort of rift in the family, probably because he didn't turn out quite as they hoped. He just disappeared after he left home.'
In 1985, Bristol's Arnolfini Gallery hosted an exhibition called Graffiti Art In Britain, at which artists sprayed paint directly on to the gallery walls and the hip hop band The Wild Bunch, which later became Massive Attack, played.
In an interview in 2006 with pop-culture magazine Swindle, Banksy said: 'I came from a relatively small city in southern England. When I was about ten years old, a kid called 3D was painting the streets hard. I think he'd been to New York and was the first to bring spray painting back to Bristol. I grew up seeing spray paint on the streets way before I ever saw it in a magazine or on a computer.
'3D quit painting and formed the band Massive Attack, which may have been good for him but was a big loss for the city. Graffiti was the thing we all loved at school. We did it on the bus on the way home from school. Everyone was doing it.'
Flower power: A double yellow line turns into a huge yellow flower - with artist 'self-portrait' - in London
Robin Gunningham left school at 16 after doing GCSEs and began dabbling in street art.
The following year, as part of Operation Anderson, undercover police arrested 72 artists across Britain on criminal damage charges. Those arrested included Tom Bingle (aka Inkie), the graffiti artist acknowledged to be Banksy's partner in crime, who is now head of creative design at the computer games manufacturer Sega. He was tried but acquitted.
Robin Gunningham was not arrested. Nor is there any record of Banksy being apprehended. But the artist has confessed he had by now become expert at evading police.
In his book Wall And Piece, he said: 'When I was 18, I spent one night trying to paint LATE AGAIN in big silver bubble letters on the side of a passenger train. British Transport Police showed up and I got ripped to shreds running away through a thorny bush. The rest of my mates made it to the car and disappeared so I spent over an hour hidden under a dumper truck with engine oil leaking all over me.
'As I lay there listening to the cops on the tracks, I realised I had to cut my painting time in half or give up altogether. I was staring straight up at the stencilled plate on the bottom of a fuel tank when I realised I could just copy that style and make each letter 3ft high.
'I got home at last and crawled into bed next to my girlfriend. I told her I'd had an epiphany that night and she told me to stop taking that drug 'cos it's bad for your heart.'
As our investigation continued, our inquiries demonstrated again and again that the details of Robin Gunningham's life story dovetail perfectly with the known facts about Banksy.
By 1998 Robin Gunningham was living in Easton, Bristol, with Luke Egan, who went on to exhibit with Banksy at Santa's Ghetto, an art store which launched at Christmas 2001 in London's West End.
Recurring motif: Another Mona Lisa in Glasgow
However, when we approached him, Egan initially denied knowing and living with either Banksy or Robin Gunningham, even though he had exhibited with the former and the electoral roll had showed him living with the latter. He eventually said: 'I lived with a guy, with Robin Gunningham. But ... '
'But you're saying he wasn't Banksy?'
'Well, he wasn't then. I lived with him ages ago. I don't think Banksy was around then anyway.'
Egan and Gunningham are believed to have left the house when the owner wanted to sell it.
Camilla Stacey, a curator at Bristol's Here Gallery who bought the property in 2000, said that Banksy and Robin Gunningham are one and the same person. She knew the house had been inhabited by Banksy because of the artwork left there - and she used to get post for him in the name of Robin Gunningham.
'I bought the house that he used to live in,' she told us. 'He had rented out a room but I think there had been problems with the tenants and the landlord had to sort of repossess it or whatever, so he was just selling it.
'When I moved in, the place had been covered in graffiti and stuff like that. I threw things in the bin.
'At that point Banksy was just someone putting up stuff around Bristol. He was just another artist who had graffitied around Bristol. It keeps me awake at night sometimes thinking about it.'
Indeed, who wouldn't regret throwing out work that would now probably fetch tens of thousands?
Suburban warrior: The semi in Bristol where Robin grew up
It was in 1998 that Banksy and Inkie collaborated with other graffiti artists on a 400-yard Walls On Fire hoarding around Bristol's Harbourside.
In local writer Steve Wright's unofficial biography, Banksy's Bristol: Home Sweet Home, Inkie said: 'I helped Banksy organise the event but took a bit of a back seat and got pretty drunk on the day if I remember rightly.'
In 1999 Banksy painted the now famous Mild Mild West sign, which shows a teddy bear with a Molotov cocktail in his hand, on a wall opposite Subway Records in Stokes Croft, Easton.
Jim Paine, founder of Subway Records, held the ladder. 'I knew Banksy from a while back, from the mid- to late Nineties when he was sharing a house in Easton, a couple of streets from me,' he said in Wright's book.
After spending some months in London, Banksy returned to Bristol in February 2000 for his first art exhibition, at the Severnshed restaurant - a former boatshed designed by Brunel. His work sold out on the opening night.
'It was the first time he had done work on canvas,' curator Robert Birse told us last week. 'He didn't have a clue how to make canvas stretch or prepare the artwork so we helped him with that side of it, but he had a very strong idea of what he wanted to do.
'I don't even know his name. He has a number of pseudonyms he gives to people he's working with, but at the time he only let his oldest mates in on everything. I presume I gave him cash [the proceeds of works he sold]. I could have written him a cheque without a name on it or I could have given him cash.'
Banksy moved to London around the turn of the millennium, once again at the same time as a certain Robin Gunningham. Robin lived in a flat in Kingsland Road, Hackney, East London, with Jamie Eastman, who worked for Bristol's Hombre record label. Banksy drew a number of the record company's album covers.
In 2001 Banksy had his first unofficial London exhibition at which he spray-painted 12 works on to the whitewashed walls of a tunnel in Rivington, Shoreditch.
But it was his show Turf War, in July 2003, held in a warehouse just yards from Robin Gunningham's flat, that put Banksy on the map.
The exhibition included live pigs and a heifer sprayed with an Andy Warhol likeness. The Queen was depicted as a chimp. An animal rights activist chained herself to the railings in protest but the RSPCA gave its approval to the show.
That same year Banksy shuffled into the Tate dressed as a pensioner and glued a picture to the wall - it stayed there for two-and-a-half hours - and demonstrated against the Iraq War. He had arrived.
He has since sold works to singer Christina Aguilera, who bought three, including a pornographic picture of Queen Victoria with a prostitute, for £25,000.
Hollywood actress Angelina Jolie blew £200,000 on his art in 2006 - among the works was a £120,000 twist on a Manet painting in which a white family lunch under an umbrella watched by 15 starving Africans.
Banksy's works have also appeared in movies such as Children Of Men and Shoot 'Em Up, and he has sold Space Girl & Bird, the artwork for Blur's Think Tank album, to a bidder from America for a record £288,000.
For someone so anonymous he has a very high profile.
But where is Robin Gunningham, the mysterious figure whose whereabouts no one now knows but who crops up in numerous official records and always in the same place as Banksy, and at the same time? The man whose photograph was recognised by his former neighbour Anthony Hallett - although the same photograph was identified by several other sources as being of Banksy? The man who Camilla Stacey, along with several other contacts who wished to remain anonymous, told us actually was Banksy?
It was time to find Robin's parents to see if they could help.
His mother Pamela lives in a neat modern bungalow in a village outside Bristol. After identifying ourselves, we asked her if she had a son called Robin.
Her reaction was very odd. We showed her the Jamaica photograph and she was visibly startled, but said she didn't recognise the man in the photograph, to whom she bears more than a passing resemblance. We asked if she could put us in touch with him.
'I'm afraid I don't know how to get in contact with him,' she said.
So she did have a son called Robin? 'No, I don't. I don't have a son at all.'
We asked her if she had any other children. 'Yes, a daughter.'
But no son and certainly not a son who went to Bristol Cathedral School?
'No,' she said, and went on to deny she was Pamela Gunningham, insisting that the electoral roll must be incorrect.
Our conversation with Peter Gunningham, who now lives in a gated development in the suburb of Kingsdown, was equally baffling.
Again, we presented the photograph of Banksy/Robin Gunningham. Mr Gunningham said he didn't recognise the person in the picture. We told him that we believed his son to be Banksy. 'No,' he replied. 'I can't help you, really.'
Mr Gunningham politely continued to deny that his son was Banksy but his manner was almost playful. He refused to give us any information about Robin. It was all very strange.
Had the couple never heard of Banksy or Robin Gunningham, one might have expected a reaction of complete bewilderment. This did not seem to be the case.
We then contacted Banksy's public relations officer who, in the best Banksy tradition, neither confirmed nor denied the story but promised to get back to us. At the time of going to press, we were still waiting to hear.
Banksy once told Swindle magazine: 'I have no interest in ever coming out. I figure there are enough self-opinionated a**holes trying to get their ugly little faces in front of you as it is.'
Given Banksy's long-standing success at covering his tracks, there is, of course, the possibility that the trail we have been following is a red herring, a complex set-up. But if it is, it must be the most elaborate such ruse ever concocted. And if it is, where is Robin Gunningham?
• Additional reporting and pictures: Simon Trump, Ewan Fletcher, Adam Luck, Jason Buckner and Craig Hibbert.