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Stephen Hawking, who sought to explain some of the most complicated questions of life while himself working under the shadow of a likely premature death, has died at 76.
The UK's Press Association reported his death, citing a spokesman for the family.
Hawking's formidable mind probed the very limits of human understanding both in the vastness of space and in the bizarre sub-molecular world of quantum theory, which he said could predict what happens at the beginning and end of time.
His work ranged from the origins of the universe itself, through the tantalising prospect of time travel to the mysteries of space's all-consuming black holes.
Prof Hawking had 12 honorary degrees, a CBE and was awarded the US Presidential Medal of Freedom in 2009.
But the power of his intellect contrasted cruelly with the weakness of his body, ravaged by the wasting motor neurone disease he contracted at the age of 21.
Hawking was confined for most of his life to a wheelchair. As his condition worsened, he had to resort to speaking through a voice synthesiser and communicating by moving his eyebrows.
The disease spurred him to work harder but also contributed to the collapse of his two marriages, he wrote in a 2013 memoir "My Brief History."
In the book he related how he was first diagnosed: "I felt it was very unfair - why should this happen to me," he wrote.
"At the time, I thought my life was over and that I would never realise the potential I felt I had. But now, 50 years later, I can be quietly satisfied with my life."
Hawking shot to international fame after the 1988 publication of "“A Brief History of Time", one of the most complex books ever to achieve mass appeal, which stayed on the Sunday Times best-sellers list for no fewer than 237 weeks.
He said he wrote the book to convey his own excitement over recent discoveries about the universe.
“"My original aim was to write a book that would sell on airport bookstalls," he told reporters at the time. "“In order to make sure it was understandable I tried the book out on my nurses. I think they understood most of it."