Tributes to Professor Stephen Hawking have been made around the world after the celebrated physicist's death at 76 was announced.
Indian prime minister Narendra Modi said Prof Hawking had "made the world a better place" and 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.
US astrophysicist Neil deGrasse Tyson was one of the first to pay tribute to Prof Hawking. Sharing a photo of himself and Prof Hawking on Twitter, he said the scientist's death has "left an intellectual vacuum in his wake".
He added: "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."
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."
Greenpeace USA thanked Prof Hawking for helping people understand their place in the universe and for "leaving us in awe and wonder".
Celebrities also paid tribute, with US singer Katy Perry saying his death left a "big black hole in my heart".
Jonathan Ross tweeted: "RIP Stephen Hawking. The world just dropped a lot of IQ points. And, he was a fun person. Very sad news."
KT Tunstall tweeted: "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."
The rock band Foo Fighters tweeted: "'Remember to look up at the stars and not down at your feet' - RIP Stephen Hawking you f****** legend."
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."
Defence Minister Tobias Ellwood said Prof Hawking "epitomised true courage over adversity as you explained the wonders of the universe to the world".
He wrote on Twitter: "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."