Stephen Hawking, whose brilliant mind ranged across time and space though his body was paralyzed by disease, died peacefully at home early Wednesday in Cambridge, England. He was 76 years old.

The best-known theoretical physicist of his time, Hawking wrote so lucidly of the mysteries of space, time and black holes that his book, A Brief History of Time, became an international bestseller, making him one of science's biggest celebrities since Albert Einstein.

In 2009, U.S. President Barack Obama presents the Medal of Freedom to Hawking at the White House. His children remembered him Wednesday as a 'great scientist and an extraordinary man.' (Chip Somodevilla/Getty Images)

"He was a great scientist and an extraordinary man whose work and legacy will live on for many years," his children Lucy, Robert and Tim said in a statement. "His courage and persistence with his brilliance and humour 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.' We will miss him forever."

Even though his body was attacked by amyotrophic lateral sclerosis, or ALS, when Hawking was 21, he stunned doctors by living with the normally fatal illness for more than 50 years. A severe attack of pneumonia in 1985 left him breathing through a tube, forcing him to communicate through an electronic voice synthesizer that gave him his distinctive robotic monotone.

But he continued his scientific work, appeared on television and married for a second time.

Sought 'theory of everything'

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.

Pope Francis greets Hawking at the Vatican in 2016. For Hawking, the search for a 'theory of everything' was almost a religious quest. (L'Osservatore Romano via Associated Press)

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.

The Universe in a Nutshell

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 Big Bang Theory, The Simpsons, Star Trek

The combination of his bestselling 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 faces.

He made cameo appearances on TV shows including The Big Bang Theory, The Simpsons and Star Trek, and counted among his fans U2 guitarist The Edge, who attended a January 2002 celebration of Hawking's 60th birthday.

Hawking delivers a lecture on the origin of the universe in Brussels in 2007. He said the question of why the universe exists 'bothers me.' (Francois Lenoir/Reuters)

His early life was chronicled in the 2014 film The Theory of Everything, with Eddie Redmayne winning the best actor Academy Award for his portrayal of the scientist. The film focused still more attention on Hawking's remarkable achievements.

"We have lost a truly beautiful mind, an astonishing scientist and the funniest man I have ever had the pleasure to meet. My love and thoughts are with his extraordinary family," Redmayne said in a statement.

Benedict Cumberbatch, the actor who starred in the 2004 BBC film Hawking — the first-ever portrayal of him onscreen — also paid tribute.

"I feel so lucky to have known such a truly great man whose profundity was found both in his work and the communication of that work," the actor said in a statement.

"'I will miss our margaritas but will raise one to the stars to celebrate your life and the light of understanding you shone so brightly on them for the rest of us."

WATCH | CBC News The National profiles Hawking in 1998

'Perfect mind trapped in an imperfect body'

Richard Green, of the Motor Neurone Disease Association — the British name for ALS — said Hawking met the classic definition of the disease, as "the perfect mind trapped in an imperfect body." He said Hawking had been an inspiration to people with the disease for many years.

Although it could take him minutes to compose answers to even simple questions, Hawking said the disability did not impair his work. It certainly did little to dampen his ambition to physically experience space himself: Hawking savoured small bursts of weightlessness in 2007 when he was flown aboard a jet that made repeated dives to simulate zero gravity.

'I have been wheelchair bound for almost four decades and the chance to float free in zero G will be wonderful. See you in zero G.' Hawking before experiencing no gravity in 2007 0:46

Hawking had hoped to leave Earth's atmosphere altogether someday, a trip he often recommended to the rest of the planet's inhabitants.

"In the long run the human race should not have all its eggs in one basket, or on one planet," Hawking said in 2008. "I just hope we can avoid dropping the basket until then."

Showed light can leave black holes

Hawking first earned prominence for his theoretical work on black holes. Disproving the belief that black holes are so dense that nothing could escape their gravitational pull, he showed that black holes leak a tiny bit of light and other types of radiation, now known as "Hawking radiation."

"It came as a complete surprise," said Gary Horowitz, a theoretical physicist at the University of California, Santa Barbara. "It really was quite revolutionary."

Horowitz said the find helped move scientists one step closer to cracking the unified theory.

Hawking's other major scientific contribution was to cosmology, the study of the universe's origin and evolution. Working with Jim Hartle of the University of California, Santa Barbara, Hawking proposed in 1983 that space and time might have no beginning and no end. "Asking what happens before the Big Bang is like asking for a point one mile north of the North Pole," he said.

In 2004, he announced that he had revised his previous view that objects sucked into black holes simply disappeared, perhaps to enter an alternate universe. Instead, he said he believed objects could be spit out of black holes in a mangled form.

That new theory capped his three-decade struggle to explain a paradox in scientific thinking: How can objects really "disappear" inside a black hole and leave no trace, as he long believed, when subatomic theory says matter can be transformed but never fully destroyed?

Diagnosed at graduate school

Hawking was born Jan. 8, 1942, in Oxford, and grew up in London and St. Albans, northwest of the capital. In 1959, he entered Oxford University and then went on to graduate work at Cambridge.

Signs of illness appeared in his first year of graduate school, and he was diagnosed with ALS, also known as Lou Gehrig's disease after the New York Yankee star who died of it. The disease usually kills within three to five years.

According to John Boslough, author of Stephen Hawking's Universe, Hawking became deeply depressed. But as it became apparent that he was not going to die soon, his spirits recovered and he bore down on his work. Brian Dickie, director of research at the Motor Neurone Disease Association, said only five per cent of those diagnosed with ALS survive for 10 years or longer. Hawking, he added, "really is at the extreme end of the scale when it comes to survival."

Hawking married Jane Wilde in 1965 and they had three children, Robert, Lucy and Timothy.

Research position in Waterloo, Ont.

Jane cared for Hawking for 20 years, until a grant from the United States paid for the 24-hour care he required.

He was inducted into the Royal Society in 1974 and received the Albert Einstein Award in 1978. In 1989, Queen Elizabeth made him a Companion of Honour, one of the highest distinctions she can bestow.

He whizzed about Cambridge at surprising speed — usually with nurses or teaching assistants in his wake — travelled and lectured widely, and appeared to enjoy his fame. He retired from his chair as Lucasian Professor in 2009 and took up a research position with the Perimeter Institute for Theoretical Physics in Waterloo, Ont.

In 2010, Prime Minister Stephen Harper sits with Hawking before making a funding announcement at the Perimeter Institute in Waterloo, Ont. (Frank Gunn/Canadian Press)

Hawking divorced Jane in 1991, an acrimonious split that strained his relationship with their children. Writing in her autobiographical Music to Move the Stars, she said the strain of caring for Hawking for nearly three decades had left her feeling like "a brittle, empty shell." Hawking married his one-time nurse Elaine Mason four years later, but the relationship was dogged by rumours of abuse.

'I ... do anything that I really want'

Police investigated in 2004 after newspapers reported that he'd been beaten, suffering injuries including a broken wrist, gashes to the face and a cut lip, and was left stranded in his garden on the hottest day of the year.

Hawking called the charges "completely false." Police found no evidence of any abuse. Hawking and Mason separated in 2006.

Hawking and his then-wife Elaine pose in front of the San Lorenzo beach in the northern Spanish city of Gijon in 2005. (Alonso Gonzales/Reuters)

Lucy Hawking said her father had an exasperating "inability to accept that there is anything he cannot do."

"I accept that there are some things I can't do," he told The Associated Press in 1997. "But they are mostly things I don't particularly want to do anyway."

Then, grinning widely, he added, "I seem to manage to do anything that I really want."