Stephen Hawking, the world-famous physicist who was walking proof any disability could be overcome, is dead, a spokesman for his family confirmed Wednesday. He was 76.

Hawking was born in Oxford, England in 1942. He was a 21-year-old Ph.D student when he was diagnosed with Amyotrophic Lateral Sclerosis (ALS), or Lou Gehrig's disease -- and told he had just a year or two to live.

He not only lived a lot longer, his 1988 book, "A Brief History of Time," explaining the mysteries of the universe in layman's language, became an international bestseller and made him an unlikely world-wide celebrity.

"For me it is quite an achievement," he said. "I never thought I could get so far."

Hawking was one of former President Obama's first recipients of the Medal of Freedom, awarded because he had overcome disability to push the boundaries of science.

"Professor Stephen Hawking is a brilliant man and a mediocre student," Mr. Obama said.

He may have been confined to a wheelchair, but his mind knew no limits. Always fascinated by space, he took a zero-gravity flight in 2007 -- the first time in 40 years he could move without the chair. He was a personality who transcended science and popular culture.

"I fit the stereotype of a disabled genius in that I'm clearly disabled but I'm not a genius like Einstein was," Hawking said.

But he was a popular genius and a media star. He had a role on "Star Trek." And he knew he had made it when his cartoon avatar had a cameo on The Simpsons.

He called the episode "very funny and now almost as many people know me through 'The Simpsons' as through my science."

He'll be remembered not just as one of the more remarkable personalities of the scientific world -- but as an inspiration figure. An authority on the past -- and the future.

"I believe that the long-term future of the human race must be in space," Hawking said. "Human race should not have all eggs in one basket, or in one planet."

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