Renowned British physicist Professor Stephen Hawking, one of the world's finest scientific minds, has died at the age of 76, a family spokesman said.
Death of a genius: Professor Stephen Hawking dies aged 76
He died peacefully at his home in Cambridge in the early hours of Wednesday morning.
In a statement, his children Lucy, Robert and Tim 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."
Astrophysicist Neil deGrasse Tyson was one of the first to pay tribute to Professor Stephen Hawking following his death aged 76.
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Sharing a photo of himself and Prof Hawking on Twitter, he said: "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."
Defence Minister Tobias Ellwood said Prof Hawking was "an inspiration to us all, whatever our station in life, to reach for the stars".
He tweeted: "RIP Sir, You epitomised true courage over adversity as you explained the wonders of the universe to the world. Your achievements symbolise the pwr of the human mind.
"An inspiration to us all, whatever our station in life, to reach for the stars-from where you now shine down on us."
Actor Macaulay Culkin described Prof Hawking as a "genius", adding that the physicist was also his favourite Simpsons character.
He tweeted: "I just heard about Stephen Hawking's passing. He was both a genius and my favorite Simpsons character. We'll miss you, buddy."
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Greenpeace USA thanked Prof Hawking for helping people understand their place in the universe and for "leaving us in awe and wonder".
Musicians also paid tribute, with KT Tunstall tweeting: "Wow. What a life. What an extraordinary Human Being. Enjoy the cosmos Stephen Hawking, the biggest and most mysterious adventure that we all get to go on one day... RIP #genius."
Sean Carroll, a physics professor at US university Caltech, said: "Stephen Hawking was the rare famous scientist who deserved every bit of his fame. A brilliant physicist and an inspirational person. And quite a character."
Jonathan Ross lamented that humankind was significantly down on intelligence points following Prof Hawking's death.
"RIP Stephen Hawking. The world just dropped a lot of IQ points. And, he was a fun person. Very sad news," the presenter tweeted.
The Twitter page for US TV show The Big Bang Theory tweeted a picture of the cast with Prof Hawking, who starred as himself in several episodes of the sitcom.
The tweet said: "In loving memory of Stephen Hawking. It was an honor to have him on The #BigBangTheory. Thank you for inspiring us and the world."
Pop superstar Katy Perry said "there's a big black hole in my heart" following Prof Hawking's death.
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Actor Kumail Nanjiani, who was nominated for an Oscar for the screenplay he co-wrote with his wife Emily V Gordon about her chronic illness, also paid tribute.
He said he was "very sad" to learn of his passing and urged fans to read A Brief History Of Time.
"It'll make the world feel more amazing and beautiful and strange. It'll also make you feel smart and stupid all at once," he added.
Indian Prime Minister Narendra Modi said Prof Hawking had "made the world a better place" and that his death was "anguishing".
"Professor Stephen Hawking was an outstanding scientist and academic. His grit and tenacity inspired people all over the world," a tweet on his page said.
"His demise is anguishing. Professor Hawking's pioneering work made our world a better place. May his soul rest in peace."
Nasa remembered Prof Hawking as a "renowned physicist and ambassador of science".
"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 organisation tweeted.
An inspiration to millions
Professor Stephen Hawking was "an inspiration to millions" and his work will leave "an indelible legacy", the University of Cambridge has said.
The acclaimed physicist died peacefully at his home in Cambridge in the early hours of Wednesday morning, at the age of 76.
Prof Hawking first arrived at the University of Cambridge in 1962 as a PhD student, and rose through the ranks to become the Lucasian Professor of Mathematics, a position once held by Sir Isaac Newton, in 1979.
He retired from this position in 2009, and became the Dennis Stanton Avery and Sally Tsui Wong-Avery Director of Research in the department of applied mathematics and theoretical physics until his death.
The university's vice-chancellor Professor Stephen Toope said: "Professor Hawking was a unique individual who will be remembered with warmth and affection not only in Cambridge but all over the world.
"His exceptional contributions to scientific knowledge and the popularisation of science and mathematics have left an indelible legacy.
"His character was an inspiration to millions. He will be much missed."
Prof Hawking was a fellow at the university's Gonville and Caius College, where a book of condolence is due to be opened.