Mr Pratt, in the old people's home, with an empty pocket

Tomorrow, 50 years after its creation, Cluedo sleuths gather for the British championships. But the real mystery is that, while Monopoly's inventor died rich and feted, the creator of the world's second most popular boardgame died poor and unknown

Bromsgrove Cemetery is not the most welcoming of places on a dark and wet autumn afternoon, but then again, you don't come to a graveyard for fun and games. Or maybe you do. After all, I was here because of Cluedo. This is where its inventor, Anthony Pratt, is buried. He should have been rich and famous except that he made a big mistake and died ordinary and forgotten in 1994. But at least he had a great epitaph, if only I could find it.

A woman bustled towards me in the rain. She looked official. "I'm here for Anthony Pratt," I said. She did not look startled. "Oh, he hasn't had a stranger visit for some time." She turned out to be Gillian Lewis, the cemetery superintendent. We talked graves: was he the only notable person buried here? "Oh, we've got a governor of North Borneo somewhere," she said distractedly. Then she asked if I'd noticed the badger. "He has moved in and is digging everywhere. The Garden of Remembrance looks like World War III!"

I found my man in a long line of other graves from 1994. His stone is grey and says: "A Very Dear Father. Anthony E Pratt. Born 10 August 1903. Died 9 April 1994. Inventor of Cluedo. Sadly missed." Later, I discovered the epitaph was his daughter's idea. "We never talked about it but I thought for purposes of posterity, it seemed right," said Marcia Davies. She is 45, works as a senior civil servant in Birmingham and the only child of Anthony and Elva Pratt. As such, she is the sole living link to the history of Cluedo.

Who knows what Anthony Pratt would make of tomorrow's Cluedo Championships at the Sherlock Holmes Hotel in Baker Street. The current champion is a man named Josef Kollar who lives in a mud-walled cottage that borders the New Forest near Southampton. He is a 53-year-old accountant who dresses up as Colonel Mustard when he plays. Mr Pratt, who had a wicked sense of humour, would probably have approved of Mr Kollar and the uniform that has been "borrowed permanently" from Salisbury Playhouse. However, in one of only two interviews during his life, Mr Pratt said that he found the game itself quite dull. So perhaps he would not fathom the "Cluedo world" that has grown up around the championships in which the characters have their very own soap opera. But first, Mr Pratt's story.

The subject of Cluedo was not talked about much in the Pratt family in later years, perhaps because he never got rich from the game that went on to become a global hit, selling millions in 23 countries, and spawning a film, stage play and television series. Marcia Davies says her parents were rather bitter about it. Certainly, Waddington's did not stay in touch. A few years ago, its PR firm launched a "Cluedo hotline" to get information about Mr Pratt on the occasion of the 150 millionth game sold. The press release was titled: "Wanted: For Murder Most Enjoyable."

But the real mystery is why the inventor of what some say is the world's second most popular board game wasn't better known by the company that had profited so handsomely from it? The inventors of Monopoly and Scrabble died multi-millionaires, their obituaries bursting with the inspiring details of rags-to-riches success. But Mr Pratt is unknown, even in his home city of Birmingham. At the city's central library, there is only one small reference. "Never heard of him," said the librarian. "Funny name, Pratt. What did you say he did? Cluedo. Hmmm."

Pratt, the younger of two sons, was born with a talent for music. He left school in his mid-teens and, as a young man, played the piano for a living, touring as part of an orchestra on ocean-liners. That's really how he should have made his name, but he was the kind of man who didn't stick with anything for long. His hobbies were more important, particularly reading. His book collection was huge and he liked psychology, crime and philosophy. He also enjoyed parties, and a party game called Murder, where guests crept up on each other and victims shrieked and fell over.

During the Second World War, he was bored doing factory duty in Birmingham. The black-out meant no parties - or games of Murder. In a 1990 interview, he said. "I was leaning on the fence of our King's Heath home and it dawned on me that this wretched old war was killing the country's social life." On the other side of the fence was his friend, Geoffrey Bull. He had invented the high-seas adventure game, Buccaneer, and sold it to Waddington's.

This inspired Mr Pratt to invent his own game. However, until now, no one has been able to say what it originally looked like.

After our interview, though, Marcia Davies went home and looked in a previously unopened box of her father's papers. There, she found the original game. It was called Murder! and set in an unnamed country house. There were 10 characters, one of which was chosen to be the victim for each game. These were Dr Black, Mr Brown, Mr Gold, the Rev Green, Miss Grey, Professor Plum, Miss Scarlet, Nurse White, Mrs Silver and Colonel Yellow. The nine weapons were an axe, a cudgel, a bomb, a rope, a dagger, a revolver, a hypodermic syringe, a bottle of poison and a poker. The original board - drawn up by Elva on their dining-room table - had a lounge, gun-room, dining-room, kitchen, ballroom, conservatory, billiard room, library, study, hall and cellar.

For a time, the Pratts and their friends spent every spare moment with murder on their minds. He demonstrated the game to Waddington's in Leeds in 1945. The company was encouraging. A few changes were made. The house was named Tudor Hall. There would be only six characters and the Colonel would have to be a Mustard. The bomb was bad news: what about a nice candlestick instead? And who needs a syringe when there is lead piping lying around? But the board, as drawn, was not altered. The agreement with Waddington's was made in 1945 but, due to a shortage of materials, it wasn't manufactured until 1949. Success was elusive. "In 1952 and 1953, Waddington's wrote that sales were not going too well," says Marcia Davies. "In May 1953, my father signed over all royalties, in respect of overseas sales, for pounds 5,000."

That was the big mistake. If he'd had even the smallest of slivers out of the overseas sales, he would have been a millionaire. "These days he would have got professional advice, of course," says his daughter. But he didn't. And, for a while, the money kept coming in. After the war, he became a civil servant but, in 1959, the Pratts moved down to Bournemouth, buying a large house with holiday flats. The British patent was due to expire in 1961 but seems to have been extended for at least four years. Mr Pratt recalled that in some quarters he would receive a large cheque, whereas at other times it would be only hundreds. "And my wife would lament that we weren't Americans who'd have made a fortune." In his papers were two other games that he submitted to Waddington's without success. One centred on buried treasure, the other on locating a gold mine.

For a while, what with the holiday flats and the Cluedo money, Anthony Pratt did not work and devoted himself to reading his Bertrand Russell, Lytton Strachey etc. He was also fond of detective stories. Sherlock Holmes, Edgar Wallace and Raymond Chandler were favourites, though he didn't rate Agatha Christie. Around Bournemouth, he could point out the scenes of notorious murders. Eventually, the cheques dwindled to the point where he went back to work, this time as a clerk in a solicitor's office. Elva liked to move and the houses got progressively smaller.

Looking back to the Sixties in a 1990 interview, Mr Pratt sounded sanguine about it all. "A letter came with a cheque and the news that there'd be no more because the patents had lapsed. That was that. We did not mind, you know. It had been one of life's bonuses. A great deal of fun went into it. So why grumble?"

This is what the company also believed, but at home there were grumbles and Marcia Davies says that the subject of Waddington's was a sore one, particularly for her mother. "Basically, they thought they'd been diddled," she says. They were not obsessed, though. Cluedo and its lessons were not the focus of their lives, which their daughter described as "very average" and fairly contented. In 1980, the Pratts moved back to Birmingham. Elva died first and Mr Pratt became forgetful, eventually developing Alzheimer's. His most prized possession, his piano, went to the old people's home with him where he died at the age of 90.

This is the fullest history that has ever appeared of Mr Pratt but, in the vacuum, myths have grown. For instance, Mr Kollar - aka Colonel Mustard - tells me that he thought that Anthony Pratt was a solicitor's clerk who'd devised the game out of real-life cases. Some say Tudor Hall is based on his own home and that Mr Pratt spent his Cluedo money touring Britain with an orchestra. Mr Kollar is interested in the real story because he is interested in all things Cluedo.

Then again, he and his wife are collectors of a great many things, including cats (seven) and records (3,000). One bedroom is crammed to bursting with his collection of 400 board-games and his wife's stuffed animals. There is only just enough space to open the door. We stand on the only visible patch of carpet and a huge yellow duck watches as we attempt to unearth the Cluedos. He shows me his Colonel Mustard uniform. The duck and I agree that it is very handsome. Eventually, we find 12 or so games and, pirouetting, ease our way out of the bedroom and back down to the lounge.

On top of the television - also an oddity in that it is a working 29- year-old ITT set - are two Cluedo trophies. There is another one on the other side of the room. Mr Kollar started dressing up as the character for the 1993 championships when participants were asked to "prove" their relationship with a character. He devised a fantastical story dating from the English Civil War involving Colonel Mustard and Mrs White and the surname Musselwhite. The story was a hit, as was the uniform. During the World Championships in New York, it even got him into the Empire State Building when it was closed. "Military types can visit any time they like," said the guard, waving him through. Colonel Mustard went up to see the view.

Mr Kollar likes the game because it involves 324 possible answers and elements of both logic and luck. "The hellish thing is you must concentrate. If you lose it, just once, you can throw yourself off completely." When he plays, he notes down every answer around the board. He keeps his own scoresheet which eventually looks like a large, logic diagram.

Unnervingly, Mr Kollar refers to the characters as if they are real. Well, maybe not real, but certainly as real as those in The Archers. "Oh, the stories about the characters have developed over the years. It's quite a little soap opera now. Miss Scarlett, as the name implies, has been in more hotel bedrooms than Gideon's Bible. As regards Mrs White, she's Dr Black's cook but prefers the brandy bottle. She is virtually permanently drunk." Mrs Peacock, he says, pretends that she's prim and proper but she's really Miss Scarlett's mother. Colonel Mustard, as it turns out, is having an affair with both of them. Not too much is known about the Rev Green. Professor Plum is a nutter, an eccentric who forgets everything.

And what of Dr Black, the eternal victim of Cluedo Not much is known about him but it seems appropriate to end this story as it, and every game of Cluedo, starts off: with a body and a mystery. Anthony Pratt would approve.