Stephen Hawking in front of the sun with coronal mass ejections. Credit:Solar & Heliospheric Observatory GHumphries@illawarramercury.com.au Another factor in Hawking's celebrity was his idea that scientists would one day discover the single "unified theory of everything". In 1988, he explored this issue in A Brief History of Time, which sold more than 25 million copies. It was a bold attempt to explain to the layman current thinking on the origins of the universe, the properties of space-time, and the search for a unified theory of physics. He concluded the book with the thought that if we do discover a complete theory of physics, we may be able to find the answer to the question of why it is that we and the universe exist. "If we find the answer to that, it would be the ultimate triumph of human reason – for then we would know the mind of God." Stephen William Hawking was born on January 8, 1942, in Oxford, the eldest son of Dr Frank Hawking, a prominent research biologist. He was brought up in St Albans where the routines of middle-class life were tempered by parental bohemianism. The family car was a London taxi and holidays were spent in a Gypsy caravan. Surprisingly slow to learn to read, Stephen was educated at St Albans School. Skinny and unco-ordinated, he was seen by his peers as the stereotypical boffin type — useless at games except cross-country running, but good at mathematics and enthusiastic (and chaotic) in chemistry. He was never top of his class, but a close friend at school recalled his "incredible instinctive insight". Faced with a complex mathematical problem, he "just knew the answer — he didn't have to think about it". It was at University College, Oxford, where he arrived in 1959, that he really blossomed. He read mathematics for a year before switching to physics. His mind, according to his tutor, was "completely different from all of his contemporaries", but he did "positively make an effort to come down to their level and be one of the boys". He was popular, and coxed the college's second rowing eight. "He did very little work, really," his physics tutor recalled, "because anything that was doable he could do".

Stephen Hawking in 1998. Credit:ABC TV After graduating in 1962, he decided to go to Cambridge for postgraduate work in cosmology. Hardly had Hawking arrived in Cambridge, to study under Dennis Sciama, then symptoms that he had first noticed at Oxford – slurred speech and trouble tying shoelaces among them – became worse. Professor Stephen Hawking, British Scientist. 1992. Credit:Photographer Unknown In 1963 he was diagnosed as suffering from a form of motor neurone disease called amyotrophic lateral sclerosis, an incurable progressive deterioration of the motor nerves that prevents muscle function, affecting speech, swallowing, and limbs, and usually ends in a fatal paralysis of the chest muscles.

For the next two years, Hawking did little research work. He spent his time in his room, listening to Wagner, reading science fiction and drinking. Then the disease seemed to stabilise, and his prospects seemed brighter. He found fresh enthusiasm and returned to work on his doctorate. He also fell in love with a language student named Jane Wilde, and they were married in 1965. Hawking described the marriage as a turning point. Apart from the disease, an added difficulty in his postgraduate research work had been finding problems suitable for someone of his ability. In 1965 Sciama found one in a paper on black holes, by the mathematician Roger Penrose. Black holes, first suggested in the 18th century, are the result of burnt-out stars collapsing under their own weight to a point so dense that nothing, not even light, can escape. The following year, in his PhD thesis Properties of the Expanding Universe, Hawking showed that the universe could have come out of a singularity without evolving perfectly smoothly. The cosmic clock could be run backwards to the Big Bang, the beginning of the universe, between 10 and 20 thousand million years ago. He showed that, if general relativity was correct, there did have to be a beginning. Hawking stayed at Cambridge after receiving his doctorate, as a fellow of Gonville and Caius College and a staff member of the Institute of Theoretical Astronomy and the Department of Applied Mathematics. In 1971, Hawking reasoned that black holes could be created other than by the collapse of massive stars, and that black holes the size of subatomic particles (and the mass of a good-sized mountain) could be left over from the big bang.

Applying quantum theory to the region surrounding such a tiny black hole, he found to his surprise that it "seemed to emit particles at a steady rate". He was reluctant to believe it at first, but finally became convinced that it was a real physical process, which happens slowly even in large black holes. Hawking delivered his mathematical evidence for this "Hawking radiation" as it is now known, at a symposium in Oxford in February 1974, to the consternation and disbelief of most of his colleagues. Although it was later confirmed by others, it still represented one of the greatest challenges ever to confront theoretical physics. Hawking's paper on the radiation from black holes was also a significant step for another reason – it combined features of quantum physics with classical general relativity, theories that are still widely regarded as almost incompatible, the former dealing with the very small and the latter with the very big. Hawking now turned to the challenge of uniting them to form a grand unified theory – a new single theory, encompassing gravity at the large scale, and the strong nuclear, weak nuclear and electromagnetic forces at the small scale – that would describe the behaviour of all the matter in the universe. In spite of his efforts, his prediction that the answer would emerge by the end of the 20th century proved wide of the mark. Hawking had been made a research assistant in the Department of Applied Mathematics and Theoretical Physics in 1973, the year he and GRF Ellis published their The Large Scale Structure of Space-Time. He became Reader in gravitational physics in 1975, and professor of gravitational physics in 1977. In 1979 he was appointed to the Lucasian chair of mathematics, a post once held by Sir Isaac Newton. For most of his life, Hawking managed to escape many of the trappings of fame, such as tabloid fascination with his private life. But this changed in 1990 when he announced he was leaving Jane, his wife of 25 years, to move in with Elaine Mason, one of his nurses, whose former husband, David, had created his voice box. The pair married in 1995.

The end of his first marriage was messy and difficult. Hawking was accused of selfishness and Elaine of marrying him so that she could bask in the reflected glory of his celebrity. In 1999, his former wife published an angry memoir Music to Move the Stars: My Life with Stephen, in which she described the daily grind of struggling to meet the demands of her three children as well as her increasingly dependent and demanding husband. Her portrait of Hawking and his new wife was not a flattering one. An "all-powerful emperor", he "had not liked being treated as but one member of the family when he considered his rightful place to be on a pedestal at the centre." In Elaine Mason, he had found someone who "was prepared to worship at his feet". No sooner had the book appeared than reports began to circulate that all was not well in Hawking's new household. By 2000 he had become a frequent visitor to Addenbrookes hospital A&E department, suffering from a series of mysterious injuries – broken bones, gashes and severe bruising. In 2004, after Hawking had once again been taken into hospital, reports appeared in the press alleging that his wife Elaine had systematically and brutally beaten, bullied, humiliated and degraded her husband over several years. No fewer than 10 nurses who had worked with Hawking were said to have come forward to allege numerous acts of cruelty. Hawking, though, consistently refused to say how he came by his injuries, or to be interviewed by police. When officers turned up at his house offering to interview him and his wife in separate rooms, he threatened to sue them for harassment. "My wife and I love each other very much," he maintained. "It is only because of her that I am alive today." In 2006, however, the couple filed for divorce. Despite all these problems, Hawking's mind remained razor sharp and his career continued to flourish. In 2002 he was awarded the Aventis Prize for Science Books for his The Universe in a Nutshell. Some colleagues found in him a self-righteous streak, and he gave few references to the work of others in his field. Others found him difficult to work with. But he never seemed to lose his sense of fun, and the mischievous glint in his eyes. In 2007 he enjoyed zero gravity on a specially organised flight in America, allowing him to float free of his wheelchair. "It was amazing," he said. "I could have gone on and on. Space, here I come."

Indeed, In 2009 Hawking was offered a place aboard a proposed commercial space flight operated by Sir Richard Branson. "I would love to go to the moon, or go into space," he said in 2015, "but I fear the doctors won't allow it." He was elected a Fellow of the Royal Society in 1974, and was appointed CBE in 1982. He was elected an Honorary Fellow of University College, Oxford, in 1977, and of Trinity Hall, Cambridge, in 1984. The Royal Society awarded him its Hughes Medal in 1976, and he was awarded numerous honorary doctorates and medals by universities and academies in Europe and the United States. He was a member of the Vatican's Pontifical Academy of Sciences from 1986. With his first wife, Jane, he had two sons and a daughter. After the end of his marriage to Elaine Mason, Hawking resumed closer relationships with his first family and in 2007 Jane revised her 1999 memoir into the less angry Travelling to Infinity: My Life with Stephen, which was subsequently made into a film as The Theory of Everything, starring Eddie Redmayne and Felicity Jones, in 2014. The Telegraph, London