Stephen Hawking released one of the most famous books in science, A Brief History of Time, in 1988. It looks into the study of the universe and has helped people around the world understand the cosmos in simple terms.
It's been translated into dozens of languages and has sold more than 10 million copies.
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However, it was almost never written.
The revolutionary thinker has battled with a disability called amyotrophic lateral sclerosis (ALS) as early as his university days at Oxford. The motor neurone disease worked gradually on the student, slowly paralysing him until he couldn't walk or talk by himself.
He was 21 years old when he was first diagnosed with ALS, with doctors giving him two years to live.
However, he cracked on with life and was determined not to let his disability get in the way. His wife at the time, Jane Hawking, was quoted as saying: "Some people would call it determination, some obstinacy. I've called it both at one time or another."
While his abilities declined over the years, it was in 1985, during a visit to CERN in Switzerland, that Hawking's health took a turn for the worse. The scientist had contracted pneumonia and he was so sick that doctors asked Jane whether they should turn off his life support.
She refused, and the only way forward was a tracheotomy - a procedure which involves making an opening on the neck to act as an airway without the use of the nose or mouth.
This is what caused Hawking to embrace his signature characteristic: his computer voice.
He first learned to communicate with others by using letters on a spelling card, however a year after his operation, he got a computer program called the 'Equalizer'. The creator, Walter Woltosz, had developed the technology to help his mother-in-law after she lost her speech to ALS.
Hawking has steadily lost more control of his body and by 2009 he could no longer drive his wheelchair.
Despite these limitations, he's written six books since his 1988 debut, co-authored five more and appeared in 14 films or series - not to mention produce four children's books with his daughter Lucy.
Stephen has also received numerous awards and accolades, with one of the most prominent being in 1974 when he was elected a Fellow of the Royal Society. He's also done countless speeches and talks about his work.
Not bad for a bloke who doctors thought wouldn't live past the age of 23.
Happy birthday Stephen, here's to many more years to come.
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