Nasa has led the tributes to Stephen Hawking, saying his "theories unlocked a universe of possibilities".
The renowned British physicist, who was one of the world's finest scientific minds, died on Wednesday at the age of 76.
Tributes poured on social media as scientists and celebrities hailed a man who had brought complex science to the masses with his best-seller "A Brief History of Time".
The US space agency described Professor Hawking as an "ambassador of science".
"Remembering Stephen Hawking, 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 the Space Station in 2014," it tweeted.
Remembering Stephen Hawking, 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 pic.twitter.com/FeR4fd2zZ5— NASA (@NASA) March 14, 2018
Lawrence M. Krauss, the theoretical physicist and best-selling author, said a "star just went out in the cosmos".
"We have lost an amazing human being. Stephen Hawking fought and tamed the cosmos bravely for 76 years and taught us all something important about what it truly means to celebrate about being human. I will miss him."
Astrophysicist Neil deGrasse Tyson said "his passing has left an intellectual vacuum in his wake".
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. pic.twitter.com/nAanMySqkt— Neil deGrasse Tyson (@neiltyson) March 14, 2018
Tobias Ellwood, the Defence Minister, 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.
The scientist's fame led to appearances on sitcoms, films about his life and music being written about him.
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.— Jonathan Ross (@wossy) March 14, 2018
Actor Macaulay Culkin described Prof Hawking as a "genius", adding that the physicist was also his favourite Simpsons character.
I just heard about Stephen Hawking's passing. He was both a genius and my favorite Simpsons character. We'll miss you, buddy.— Macaulay Culkin (@IncredibleCulk) March 14, 2018
Errol Morris, who made a biographical documentary film called A Brief History of Time, said he was "funny, perverse, and, of course, brilliant".
It had to happen, eventually. We were lucky to have him for so long, and I was lucky to be able to work with him. A truly fabulous human being. Stephen Hawking. Funny, perverse, and, of course, brilliant.— errolmorris (@errolmorris) March 14, 2018
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."