Theresa May has been joined by leading scientists and figures from the entertainment industry in paying tribute to Professor Stephen Hawking who died this morning.
The Prime Minister said in a tweet that Professor Hawking was "one of the greatest scientists of his generation" and "his legacy will not be forgotten".
The 76-year-old, whose life's work shaped modern cosmology and helped ordinary people to better understand the universe, passed away in the early hours of this morning, his family confirmed.
Professor Hawking's "A Brief History of Time" was published in 1988 and entered the Guinness Book of Records after staying on The Sunday Times bestseller list for 237 weeks.
The book sold 10m copies and was translated into 40 different languages, but is famously referred to as one of the "greatest unread books in history".
Eddie Redmayne, who won an Oscar for his portrayal as the physicist in The Theory Of Everything, said in a statement: "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."
British astronaut Tim Peake tweeted that Professor Hawking "inspired generations to look beyond our own blue planet and expand our understanding of the universe".
Physicist and television personality Professor Brian Cox wrote: "What a remarkable life.
"His contributions to science will be used as long as there are scientists, and there are many more scientists because of him."
Professor Hawking contracted motor neurone disease in 1963 aged 21.
Despite doctors giving him just two years to live, he went on to study cosmology at Cambridge and became one of the most brilliant theoretical physicists since Albert Einstein.
At the age of 37 Hawking was the Lucasian professor of mathematics at Cambridge, a chair formerly held by Isaac Newton and the "father of the computer" Charles Babbage.
For much of his time in the public eye his illness confined him to a wheelchair and, from 1985, he communicated through a computer.
The Motor Neurone Disease Association's website went down earlier after an influx in donations after Professor Hawking's death.
American astrophysicist Neil deGrasse Tyson tweeted: "His passing has left an intellectual vacuum in his wake.
"But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure.
"Stephen Hawking, RIP 1942-2018."
Comedy actor David Walliams has also paid tribute to Professor Hawking, with the physicist having appeared in his sketch show Little Britain.
He wrote: "Goodbye #StephenHawking Thank you for being - amongst everything else - a great laugh."
Microsoft CEO Satya Nadella said on Twitter that "we lost a great one today" and added: "Stephen Hawking will be remembered for his incredible contributions to science - making complex theories and concepts more accessible to the masses."
Professor Hawking's children, Lucy, Robert and Tim, said in a statement that he had died at his home in Cambridge in the early hours of Wednesday.
They said: "We are deeply saddened that our beloved father passed away today.
"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 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."
They asked for privacy but added their thanks to "everyone who has been by Professor Hawking's side and supported him - throughout his life".
The world-renowned astrophysicist was given more than a dozen honorary degrees in his career and was awarded a CBE in 1982.
It was his 1988 book A Brief History Of Time that cemented his position as perhaps the best-known scientist of his time.
Professor Hawking's first attempt to write a popular book about the physics and the universe's beginnings was a massive success, spending 237 weeks on the Sunday Times best sellers list.
His life was retold in the 2014 film The Theory Of Everything, which starred Eddie Redmayne and Felicity Jones.
Professor Hawking, who became renowned for his sense of humour, also performed cameos in the US comedy series The Big Bang Theory as well as The Simpsons and Star Trek.
But in between his screen appearances, his amazing mind tackled everything from the origins of the universe to the possibility of time travel and the mystery of the solar system's black holes.
He once described belief in a God who intervenes in the universe "to make sure the good guys win or get rewarded in the next life" as 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 University of Cambridge will open a book of condolence at Gonville and Caius College.