In 1999, CNN's Larry King introduced Stephen Hawking to television viewers as the man 'who can sell physics better than Madonna can sell sex'. When you consider that his book A Brief History of Time, published in 1988, sold 9 million copies by 2002 and was on the London Sunday Times best-sellers list for a record-breaking 237 weeks, the description could well be right. Dubbed by some as the 'unread best-seller', the book has, nevertheless, served to popularise some of the more arcane notions of theoretical physics. Black holes and the big bang are almost household phrases because of it. Notwithstanding the fact that most of the 64-year-old professor's work is mathematical in nature, there's hardly an equation in sight in A Brief History, which helps its popularity, but you might still well ask why a book on such abstruse material would grace so many bookshelves, read or not. Professor Yau Shing-tung, director of Chinese University's Institute of Advanced Mathematical Sciences and chair of Strings 2006 - a six-day conference on string theory in Beijing next week that Professor Hawking is due to address - has no doubt about the physicist's appeal. He says Hawking is blessed with a sense of humour and the rare ability to communicate difficult ideas in a popular way that strikes a chord with the layman. 'That's one of the reasons why we invited him to China this year,' he said. 'We respect Stephen as a physicist and wanted him to come and give a talk because of that, but we also wanted to exploit the fact that he's extremely famous and can talk to a general audience and excite the general layman about general theoretical physics, which has not been as popular in China as in other countries.' If most people outside the classroom are familiar with the concept of the big bang or know what black holes are, odds are it will be because of Professor Hawking's popularising. There are, after all, any number of scientific concepts equally as important to cutting-edge research that are completely unknown outside of higher academia. Humour and the simple approach are his stock in trade. There are countless examples of the Hawking soundbite scattered through his work, usually falling at just the right moment to add light relief to a particularly heavy theme. Take black holes, for example. Having revised his opinion of whether it would be possible to travel in space and time, he compared such a journey through a black hole to 'going over Niagara in a barrel', during a lecture entitled Black Holes and Baby Universes, at the University of California, Berkeley, in 1988. 'Black holes might be useful for getting rid of garbage or even some of one's friends,' he wrote, but they were 'a country from which no traveller returns'. Another memorable soundbite was Professor Hawking's take on Einstein's famous phrase, 'God does not play dice'. Talking about the difficulty of predicting anything about the particles emitted by black holes (known as Hawking Radiation), he said in 'The Quantum Mechanics of Black Holes', published in Scientific American in 1977: 'Consideration of particle emission from black holes would seem to suggest that God not only plays dice but also sometimes throws them where they cannot be seen.' And then there are the bets. One of the best ways to remember whether the star system Cygnus X-1 is a black hole is to recall that Professor Hawking lost a famous bet over it. Despite all his work on the subject, he wagered his colleague Kip Thorne in Caltech, after the discovery of Cygnus by X-ray astronomy in the 1970s, that it would not turn out to be a black hole. He explained that this was by way of 'insurance': if he lost, his black hole theory stood up. If he won, on the other hand, he would get a subscription to satirical magazine Private Eye. He lost and it cost him a year's subscription to Penthouse magazine. Later, he and Professor Thorne bet their colleague John Preskill that information was lost in black holes. When he discovered they 'evaporated' radiation he again paid up, this time providing an encyclopedia of baseball 'where information can be recovered at will'. And then there are the countless anecdotes. He's said not to suffer fools gladly and to have occasionally run over the foot of an adversary or two with his wheelchair to make the point. On another occasion, Bantam Books editor Peter Guzzardi was reported, on meeting Professor Hawking for the first time, to have gushed at length about what an honour it was to meet the great scientist, when he was interrupted by strange noises coming from the direction of the wheelchair. A graduate helper is said to have translated: 'Professor Hawking says, 'Where's the contract?'' Stories also abound regarding his alleged eye for the fairer sex. Asked by King during the 1999 interview what puzzled him and what he thought about most, he answered, 'Women.' CUHK's Professor Yau has an anecdote closer to home. He recalls how, when he brought Professor Hawking to China for an earlier string theory conference in 2002, he'd promised to keep the press away from him. 'In Hangzhou, all the TV stations wanted to interview him, but he was worried about getting too tired, so we stopped it,' he said. 'Phoenix TV had a very beautiful anchor woman. She interviewed me first and then wanted to interview Professor Hawking. I said, 'I can't allow you to do that because I promised Stephen', but she insisted. 'How do you deal with a beautiful woman? Well, I said OK, he's talking with my friends about physics. You can try your luck and pass by there and show yourself off. I think he may be interested to talk to a beautiful woman.' Professor Yau said she went over and gave the physicist a hug, 'which worked very well'. An interview lunch was arranged, with the students offering to act as translators. 'I learned about it at dinner time and I said jokingly with Stephen's wife [Elaine Hawking] there, 'Stephen's got an interview with a beautiful woman.' For some reason it was cancelled after that!' Professor Yau said he hadn't been sure at first how Professor Hawking's popularising style would be received on the mainland, especially because he was paralysed after being diagnosed with a form of motor neurone disease at the age of 21, when he was studying for his PhD at Cambridge University. 'To be frank, I was not sure the Chinese would be as crazy about him as Americans or British because of anxiety about his condition, but I was surprised. Chinese students and ordinary people were really hot on him, treating him like a rock star. We put him in a big stadium in Hangzhou and 3,000 people came to listen, some from very far away. Many couldn't get in and besieged the place shouting 'Hawking, Hawking, Hawking'. 'We gave out free tickets so we could manage the event, but they were going for 100 yuan each on the black market.' Despite the jokes, bets and anecdotes, however, it's the cutting-edge science for which Professor Hawking, who holds the Lucasian Chair of Mathematics at Cambridge - the position once held by Isaac Newton - will be remembered. Professor Yau, who has known Professor Hawking since 1978, said he considered his work on the concept of quantum gravity to be a major contribution. 'He gave the first successful indication of the possibility of quantum gravity with its formula on entropy and the black hole evaporation process,' he said. 'It's a major accomplishment - a clear concept that can even be tested.' And Michael Wong Kwok-yee, an associate professor at Hong Kong University of Science and Technology, where Professor Hawking is due to give a lecture, The Origin of the Universe, this afternoon - for which all tickets have been snapped up - said he would be remembered for combining quantum mechanics and general relativity. 'He's famous for Hawking Radiation and for combining quantum mechanics and general relativity. These two fields are the most important in 20th-century physics, but seem to have two separate sets of laws that don't have anything in common. Many scientists have tried to combine them. 'People believe you need to combine these two for cosmology - a study of the early universe,' Dr Wong said. 'In the early stage of the big bang, space was so confined and the density was so high that you have to consider both. You have to consider relativity because you have high density, but because it's so small you have to consider quantum effects.' But perhaps the last word should go to Professor Hawking himself. Writing of his achievements in his book Black Holes and Baby Universes and Other Essays, he said: 'I wanted to fathom the far depths of the universe. Maybe I have succeeded to a small extent, but there's still plenty I want to know.' In a later essay in the same book, he added: 'Although science may solve the problem of how the universe began, it cannot answer the question: Why does the universe bother to exist? I don't know the answer to that.'