(CBSNEWS) – Stephen Hawking, the world-famous physicist who deepened our understanding of the universe while proving that any disability could be overcome, has died, a spokesman for his family confirmed Wednesday. He was 76. His three children Lucy, Robert and Tim, said in a statement, “We will miss him forever.”

“We are deeply saddened that our beloved father passed away today,” his children said in a statement. “He was a great scientist and an extraordinary man whose work and legacy will live on for many years. His courage and persistence with his brilliance and humor inspired people across the world. He once said, ‘It would not be much of a universe if it wasn’t home to the people you love.'”

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.

Although he would be confined to a wheelchair and largely unable to speak except through a voice synthesizer, he lived a lot longer than that.

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. The book sold more than 10 million copies.

As one of Isaac Newton’s successors as Lucasian Professor of Mathematics at Cambridge University, Hawking was involved in the search for the great goal of physics — a “unified theory.”

Such a theory would resolve the contradictions between Einstein’s General Theory of Relativity, which describes the laws of gravity that govern the motion of large objects like planets, and the Theory of Quantum Mechanics, which deals with the world of subatomic particles.

For Hawking, the search was almost a religious quest — he said finding a “theory of everything” would allow mankind to “know the mind of God.”

“A complete, consistent unified theory is only the first step: our goal is a complete understanding of the events around us, and of our own existence,” he wrote in “A Brief History of Time.” When he turned 60, he spoke to Ed Bradley on “60 Minutes.”

“For me it is quite an achievement,” he told Bradley. “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 disable genius in that I’m clearly disabled but I’m not a genius like Einstein was,” Hawking told Bradley

In later years, though, he suggested a unified theory might not exist.

He followed up “A Brief History of Time” in 2001 with the more accessible sequel “The Universe in a Nutshell,” updating readers on concepts like super gravity, naked singularities and the possibility of an 11-dimensional universe.

Hawking said belief in a God who intervenes in the universe “to make sure the good guys win or get rewarded in the next life” was wishful thinking.

“But one can’t help asking the question: Why does the universe exist?” he said in 1991. “I don’t know an operational way to give the question or the answer, if there is one, a meaning. But it bothers me.”

The combination of his best-selling book and his almost total disability — for a while he could use a few fingers, later he could only tighten the muscles on his face — made him one of science’s most recognizable figures.