Professor Stephen Hawking, the famed theoretical physicist and author, has died aged 76.

Prof. Hawking, who defied a debilitating disease to become one of the greatest scientists in history, died at his home in Cambridge this morning.

"We are deeply saddened that our beloved father passed away today," his children Lucy, Robert and Tim said in a statement.

"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."

Professor Stephen Hawking has died aged 76.

Professor Hawking in New Jersey in 1979. (AAP) (Getty)

Prof. Hawking was born in Oxford in 1942 to medical researcher Frank and secretary Isobel Hawking.

The couple had been living in London but moved to Oxford to find greater safety during World War II.

He was diagnosed with amyotrophic lateral sclerosis (ALS) - a form of motor neurone disease - in 1963 aged 21 and was just given two years to live.

But the disease that progressed slower than usual and he went on to live for more than half a century, making discoveries that changed how we see the universe.

A severe attack of pneumonia in 1985 left him breathing through a tube, forcing him to communicate through an electronic voice synthesiser that gave him his famous robotic monotone.

The synthesiser was controlled by a single muscle in his cheek.

Professor Hawking on stage during the New Space Exploration Initiative's "Breakthrough Starshot" announcement at One World Observatory in New York City in 2016. (Jemal Countess/Getty Images) (Getty)

Professor Hawking and his first wife Jane at the 'The Theory of Everything' film premiere. (Getty)

Professor Hawking was was responsible for numerous breakthroughs in physics and cosmology. (Supplied) (Supplied)

One of his first breakthroughs came in 1970, when he and fellow physicist Roger Penrose proposed four laws of black hole mechanics.

Prof. Hawking married Jane Wilde, a friend of his sister's, in 1965. The couple had three children together before divorcing in 1995.

That same year he married one his nurses, Elaine Mason. The couple divorced in 2006.

Prof. Hawking wrote the immensely popular 1988 book A Brief History of Time , which delved into the origins and structure of the universe in terms readily understood by non-experts.

'The Theory of Everything' stars Felicity Jones and Eddie Redmayne with Hawking in 2014. (AAP) (AAP)

The book sold more than 10 million copies and was translated into at least 35 languages.

"My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all," Prof. Hawking once said of his quest for knowledge.

He said belief in a God who intervenes in the universe "to make sure the good guys win or get rewarded in the next life" was wishful thinking.

"But one can't help asking the question: why does the universe exist?" he said in 1991.

"I don't know an operational way to give the question or the answer, if there is one, a meaning. But it bothers me."

In his 2013 autobiography My Brief History , Prof. Hawking revealed his feelings of despair after his diagnosis.

"I felt it was very unfair – why should his happen to me?" he wrote.

"At the time, I thought my life was over and that I would never realise the potential I felt I had.

"But now, 50 years later, I can be quietly satisfied with my life."

Prof. Hawking's early life was dramatised in the 2014 film The Theory of Everything , starring Eddie Redmayne and Felicity Jones.

Redmayne, who portrayed Prof. Hawking, won the Academy Award for Best Actor for his performance.

Prof. Hawking was an Honorary Fellow of the Royal Society of Arts, a lifetime member of the Pontifical Academy of Sciences, and was a recipient of the Presidential Medal of Freedom, the highest civilian award in the US.

He was the Lucasian Professor of Mathematics at the University of Cambridge from 1979 to 2009 - a title previously held by Sir Isaac Newton, among others.

Tributes from fellow scientists, authors, fans and thought leaders have begun to flow on social media.