In his final years, the only thing connecting the brilliant physicist to the outside world was a couple of inches of frayed nerve in his cheek.
As slowly as a word per minute, Stephen Hawking used the twitching of the muscle under his right eye to grind out his thoughts on a custom-built computer, painstakingly outlining his vision of time, the universe, and humanity's place within it.
With his brilliant mind ranged across time and space, Stephen Hawking was Britain's most famous modern-day scientist, a genius who dedicated his life to unlocking the secrets of the universe. On Wednesday, one of the greatest minds of history died peacefully at his home in Cambridge, England at the age of 76.
Born on Jan. 8, 1942 - 300 years to the day after the death of the father of modern science, Galileo Galilei - he believed science was his destiny.
But fate also dealt Hawking a cruel hand. His body was attacked by amyotrophic lateral sclerosis (ALS), a form of motor neuron disease that attacks the nerves controlling voluntary movement, when Hawking was 21. Remarkably, Hawking stunned doctors, defied predictions that he would only live for a few 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 and live his life as full as possible.
"I am quite often asked: How do you feel about having ALS?" he once wrote. "The answer is, not a lot.
"I try to lead as normal a life as possible, and not think about my condition, or regret the things it prevents me from doing, which are not that many."
Stephen William Hawking, though, was far from normal.
Inside the shell of his increasingly useless body was a razor-sharp mind, fascinated by the nature of the universe, how it was formed and how it might end.
"My goal is simple," he once said. "It is the complete understanding of the universe, why it is as it is and why it exists at all."
Much of that work centered on bringing together relativity - the nature of space and time - and quantum theory - how the smallest particles in the universe behave - to explain the creation of the universe and how it is governed.
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.
Hawking married Jane Wilde in 1965 and they had three children, Robert, Lucy and Timothy.
The couple split after 25 years and he married his former nurse, Elaine Mason, but the union broke down amid allegations, denied by him, of abuse.
Life on Earth at risk
In 1974, he became one of the youngest fellows of Britain's most prestigious scientific body, the Royal Society, at the age of 32.
Hawking received the Albert Einstein Award in 1978. In 1979 he was appointed Lucasian Professor of Mathematics at Cambridge University, where he had moved from Oxford University to study theoretical astronomy and cosmology.
A previous holder of the prestigious post was the 17th-century British scientist Isaac Newton.
He whizzed about Cambridge at surprising speed - usually with nurses or teaching assistants in his wake - traveled and lectured widely.
Hawking eventually put Newton's gravitational theories to the test in 2007 when, aged 65, he went on a weightless flight in the U.S. as a prelude to a hoped-for sub-orbital spaceflight.
Characteristically, he did not see the trip as a mere birthday present.
Instead, he said he wanted to show that disability was no bar to achievement and to encourage interest in space, where he believed humankind's destiny lay.
"I think the human race has no future if it doesn't go into space," he said.
"I believe life on Earth is at an ever-increasing risk of being wiped out by a disaster such as sudden global warming, nuclear war, a genetically engineered virus or other dangers."
More recently he said artificial intelligence (AI) could contribute to the eradication of disease and poverty while warning of its potential dangers.
"In short, success in creating AI could be the biggest event in the history of our civilization.
"Alongside the benefits, AI will also bring dangers, like powerful autonomous weapons, or new ways for the few to oppress the many," Hawking said in 2016, at the opening of a new AI research center at Cambridge University.
Theories on black holes
Theoretical physicist Stephen Hawking poses during a photo call for a gala screening of the documentary "Hawking," a film about the scientist's life, Cambridge, Britain.
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?
Pop culture and politics
Hawking's genius brought him global fame and he became known as a witty communicator dedicated to bringing science to a wider audience.
His 1988 book "A Brief History of Time" sought to explain to non-scientists the fundamental theories of the universe and it became an international bestseller, bringing him global acclaim.
It was followed in 2001 by "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."
In 2007, Hawking published a children's book, "George's Secret Key to the Universe," with his daughter, Lucy, seeking to explain the workings of the solar system, asteroids, his pet subject of black holes and other celestial bodies.
Hawking also moved into popular culture, with cameos in "Star Trek: The Next Generation" and "The Simpsons," while his voice appeared in Pink Floyd songs.
Beyond scientific debate Hawking also weighed into politics, describing Donald Trump as "a demagogue who seems to appeal to the lowest common denominator" ahead of his election as U.S. president.
Hawking also warned Britain ahead of the Brexit referendum in 2016 against leaving the European Union: "Gone are the days when we could stand on our own against the world."
Making the most of 'every minute'
The wedding photo of Stephen Hawking and his first wife Jane Wilde in 1965.
The love story between Hawking and Wilde, his first wife, was retold in the 2014 film "The Theory of Everything," which won Britain's Eddie Redmayne the best actor Oscar for his portrayal of the scientist.
The Oscar triumph was celebrated by Hawking, who has reportedly said there were moments watching the film when he thought he was watching himself.
He was also the subject of a 2013 documentary, "Hawking," in which he reflected on his life: "Because every day could be my last, I have the desire to make the most of each and every minute."