The Motor Neurone Disease Association has said it has seen an "influx of donations this morning" following the death of Prof Hawking - so many in fact that its website has crashed.

The charity said Prof Hawking "played a vital role" in raising awareness of the disease, which kills more than half of people within two years of diagnosis.

London's National Portrait Gallery commissioned a painting of Prof Hawking in 1985 - three years before he achieved fame with his bestselling book, A Brief History of Time.

The gallery has paid tribute to him with a tweet of the portrait.

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Professor Sir Alan Fersht, who is master of Gonville and Caius College, Cambridge, says Professor Hawking remained a visitor to his old college.

"Being master of the college, I saw quite a lot of him. He loved to come into college.

"College is a fun place. We dine most evenings. The students are stretched out in hall like in Hogwarts.

"We dine on high table and Stephen would love coming in with his carers to high table and join in with the rest of us.

"He'd go to parties, dance in his wheelchair. Real lively individual."

To celebrate Stephen Hawking's Radio 4 Reith Lecture on black holes in 2016, the BBC made an audacious attempt to journey into the mind of the world's most famous physicist.

With a little bit of help from Aardman Studios, Carl Sagan, Professor Brian Cox, US theoretical physicist Andrew Strominger and, of course, the man himself, this is what we came up with.

In 2016, Professor Stephen Hawking delivered two BBC Reith Lectures on black holes - where he explained the scientific thinking, how they have posed tough challenges to conventional understanding of the laws which govern the universe, and also asked a slightly more intriguing question: Do black holes have no hair?

His second lecture looked at why black holes aren't as black as they are painted.

"It would not be much of a universe if it wasn't home to the people you love," his family say in a statement quoting Prof Hawking.

As the tributes pour in, the BBC's Francesca Gillett gathers them all up for you in one piece.

Professor George Smoot, a friend and colleague of Stephen Hawking, tells the BBC that the two men had recently discussed the opportunities for experiencing zero-gravity (something Professor Hawking did in 2007) or going into space.

He said the physicist had always tried to fight the disease that was killing him.

"The reason he wanted to do Zero-G and he didn't want to go into space was because that got him the chance to be like a normal human being.

"Because, no longer is gravity restraining you, you can float around and ... flying like you're in a dream and it was very interesting how he was trying to live as normal a life as possible.

Image source, AFP

"He did great science and it was the disease - the fact that he had the disease that threatened to take his life in a short-time - which he resisted fiercely so he's a hero for doing that.

"Once he was diagnosed he started to get down and get really serious in saying, you know: I have these gifts and these skills, I should use it."

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Lucy Hawking describes the moment her famous scientist father was asked by a child - what happens if you fall into a black hole?

"As a child you could ask any question you wanted - and get a reply," she said.

Image source, PA

Eddie Redmayne, who won an Oscar for his portrayal of Prof Hawking in the 2014 film The Theory Of Everything, has paid tribute to "the funniest man".

In a statement, the actor 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."

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Image source, PA

British physicist Brian Cox says Professor Hawking, who he last saw at his 75th birthday party, was "one of the greats".

"There are many good theoretical physicists - but there aren't many greats."

He says he read A Brief History of Time at the age of 20 and was struck by the mixture of brilliance in physics and the sense of wonder and possibility.

He was telling us we could understand the universe, says Professor Cox.

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Mexican-British cosmologist Carlos Frenk says Prof Hawking was a man who changed the panorama of theoretical physics.

His disability forced him to invent a new way to express himself making his work unique yet his imagination was unbounded, he adds.

He was trapped in his body but free in his mind, says Prof Frenk, who is one of the Gang of Four who worked out 30 years ago that the universe is full of cold dark matter.

Stephen Hawking's name is top of Twitter's worldwide trending list, with more than two million tweets posted since his death was announced.

Prime Minister Theresa May pays tribute to Stephen Hawking, saying he was "a brilliant and extraordinary mind - one of the great scientists of his generation".

Image source, AFP

Martin Rees, Astronomer Royal, Fellow of Trinity College, and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge, has been paying tribute to Stephen Hawking.

"Tragedy struck Stephen Hawking when he was only 22. He was diagnosed with a deadly disease, and his expectations dropped to zero. He himself said that everything that happened since then was a bonus," Prof Lord Rees said.

"And what a triumph his life has been. His name will live in the annals of science; millions have had their cosmic horizons widened by his best-selling books; and even more, around the world, have been inspired by a unique example of achievement against all the odds - a manifestation of amazing willpower and determination."

Prof Hawking died on Albert Eistein's birthday, a day also named after the mathematical constant pi - the first three numerals of which are 3.14.