Eddie Redmayne has led tributes to Professor Stephen Hawking following the physicist's death at 76, describing him as "the funniest man" he has ever met.
The actor, who won an Oscar for his portrayal of Prof Hawking in 2014 film The Theory of Everything, said: "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."
The wheelchair-confined scientist passed away peacefully at his home in the early hours of Wednesday, his family said.
Within hours of the announcement, tributes were pouring in from around the globe - not just from scientists but also actors, musicians, charities and politicians.
Prof Hawking's career looked like being cruelly cut short in 1964 while he was still studying for his PhD at Cambridge University. He was diagnosed with a rare form of motor neurone disease and given just a few years to live.
His illness left him crumpled in a wheelchair and dependent on a computerised voice system for communication.
Yet, defying all expectations, he went on to become a towering figure in the world of physics, a bestselling author, a father of three and a TV celebrity.
His book A Brief History of Time, published in 1988 - in which he explained the Big Bang and black holes in simple terms, was an unlikely megahit, selling more than than 10 million copies.
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."
Benedict Cumberbatch also paid tribute to Prof Hawking - who he played on screen - calling him "a true inspiration for me and for millions".
Cumberbatch starred as the scientist in the first portrayal of him on-screen before Redmayne took on the role.
The Sherlock actor, who played Prof Hawking in the TV film Hawking in 2004, said he was "so sad to hear that Stephen has died" and that he would raise a margarita, which they once shared together, "to the stars".
"I feel so lucky to have known such a truly great man whose profundity was found both in his work and the communication of that work," he said.
"He virtually created the publishing genre of popular science, a heroic feat to bring the wondrous complexities of the universe to all outside of specialists in this field.
"It was truly courageous considering it was achieved by a man who lived a life trapped in his body from the age of 21 when he was diagnosed with motor neurone disease.
"His support of the sciences, art, education and charities such as the MND foundation will also live on, as will his wickedly funny sense of humour.
"I will miss our margaritas but will raise one to the stars to celebrate your life and the light of understanding you shone so brightly on them for the rest of us.
"You were and are a true inspiration for me and for millions around the world. Thank you."
Former US president Barack Obama also paid tribute to Prof Hawking, who he once awarded America's highest civilian honour.
"Have fun out there among the stars," he wrote alongside a photo of himself speaking with the physicist at the White House.
In 2009, the then president awarded him the Presidential Medal of Freedom.
British prime minister Theresa May was among others to pay tribute.
"Professor Stephen Hawking was a brilliant and extraordinary mind - one of the great scientists of his generation," she said.
"His courage, humour and determination to get the most from life was an inspiration. His legacy will not be forgotten."
Scientist and broadcaster Professor Brian Cox said Prof Hawking was "one of the greats".
"There are many good theoretical physicists who make a big contribution, but there aren't that many greats," he said.
"By that I mean that I think there are physicists in a thousand years' time, they will still be talking about Hawking radiation, they will be using his fundamental results on black holes.
"Actually, the last time I saw him, at his 75th birthday party, he was talking about the new gravitational wave experiment where we've seen the collisions of black holes, and speculating that those results might be able to prove some of his theorems once and for all.
"Plus his contributions to the physics of the very early universe, so there are at least three and possibly more areas where his work will be remembered as long as there are cosmologists, and that's the best you can hope for as a scientist."
The Big Bang Theory's Johnny Galecki wrote on Instagram: "RIP #stephenhawking. Not only your brilliance, but your sense of humour will be sorely missed by all."
Like the mathematics Prof Hawking grappled with from his wheelchair, his domestic life was complicated.
In February 1990, after 25 years of marriage, he left the wife who bore him three children to set up home with one of his nurses, Elaine Mason. The couple married in September 1995, but divorced in 2006.
Prof Hawking was no stranger to controversy and seemed to relish it.
His proposal that black holes could lose energy and evaporate contradicted the prevailing view that nothing could escape from one of the infinitely dense regions of space-time.
"Hawking Radiation" was a brilliant concept, but remains unproven by observation. For this reason the greatest scientific prize of all, the Nobel, eluded Prof Hawking up to the time of his death.
Later in his career, he ruffled academic feathers with bizarre statements about extraterrestrials, time travel, and human genetic engineering.