LONDON — Tributes from around the world poured in Wednesday for Stephen Hawking, one of the world’s most famous scientists, who died age 76.

Hawking, an intellectual giant who became an international symbol of the power of the human mind, died peacefully at his home in Cambridge, England.

The celebrated British physicist probed the mysteries of the cosmos and helped to popularize science with books like “A Brief History of Time,” an international bestseller.

When he was just 21, he was diagnosed with a rare form of motor neuron disease and told by doctors he had only a few years to live. His illness left him unable to move a muscle and he could only talk with the help of a voice synthesizer.

On Wednesday morning, “Stephen Hawking” was trending worldwide on social media.

In a statement his children, Lucy, Robert and Tim, said that their father was a “great scientist and an extraordinary man.” They added: “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.”

NASA, the U.S. space agency, tweeted: “His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity, as you said to astronauts on @Space_Station in 2014.”

The founder of the World Wide Web, Tim Berners-Lee said: “We have lost a colossal mind and a wonderful spirit.”

Canadian astronaut Chris Hadfield tweeted: “Genius is so fine and rare. Goodbye Professor Hawking. You inspired and taught us all.”

The University of Cambridge, Hawking’s academic home, tweeted a video tribute while his college at the university opened a book of condolences.

“We lost a great one today,” wrote Satya Nadella, the CEO of Microsoft.

The astrophysicist Neil deGrasse Tyson said his passing had “left an intellectual vacuum.”

Martin Rees, former president of the Royal Society, Britain’s leading scientific body, said in a statement: “Soon after I enrolled as a graduate student at Cambridge University in 1964, I encountered a fellow student, two years ahead of me in his studies; he was unsteady on his feet and spoke with great difficulty. This was Stephen Hawking.”

“He had recently been diagnosed with a degenerative disease, and it was thought that he might not survive long enough even to finish his PhD. But, amazingly, he lived on to the age of 76.  Even mere survival would have been a medical marvel, but of course he didn’t just survive.  He became one of the most famous scientists  in the world — acclaimed as a world-leading researcher in mathematical physics, for his best-selling books about space, time and the cosmos, and for his astonishing triumph over adversity.”

It wasn’t just the scientists that mourned his passing, but tributes came from 10 Downing Street as well, where the prime minister’s account celebrated him as an “inspiration” and one of the “great scientists of his generation.”

Hawking also was a cultural phenomena, appearing on shows like The Simpsons and The Big Bang Theory as well as an episode Star Trek: The Next Generation in which he played poker with actors portraying Albert Einstein and Isaac Newton. Films were also made about his life, including “The Theory of Everything,” which saw Eddie Redmayne win an Oscar for his portrayal of Hawking.

Redmayne said on Wednesday: “We have lost a truly beautiful mind, an astonishing scientist and the funniest man I have ever had the pleasure to meet.” (Hawking once joked that “unfortunately Eddie did not inherit my good looks.”)

Hawking was also known for his wit and sense of humor. “I think my work and sense of humor have kept me going,” Hawking said, during his BBC Reith Lecture series in 2016.

“It’s important not to become angry no matter how difficult life may seem because you can lose all hope if you can’t laugh at yourself and laugh in general,” he said.

A BBC reporter shared this story of Hawking at the BBC.

Jonathan McDowell, an astrophysicist at Harvard, recalled that when he gave lectures he would add in jokes even when it was difficult for him to speak.

He also noted an extra significance of the date.