One of the most recognisable faces of science, Stephen Hawking's life and work has fascinated people for decades. Here are ten key facts about the scientist, on his 75th birthday:
1. Hawking was born on 8 January 1942 in Oxford and grew up in St Albans, as the eldest of four siblings. His father was a research biologist and his mother was a medical research secretary. His birth date is also the 300th anniversary of the death of physicist Galileo Galilei.
2. In 1959, Hawking began his university education at University College, Oxford, at the age of 17. Although he wanted to study mathematics, it was not available at the university so he read physics instead, receiving a first class honours degree in natural science.
3. Hawking, who has 12 honorary degrees, was awarded the CBE in 1982 and is a Fellow of The Royal Society and a Member of the US National Academy of Science.
4. Hawking was diagnosed with ALS, amyotrophic lateral sclerosis or Lou Gehrig's disease, at the age of 21. He has a rare, slow-progressing form of ALS, which has gradually paralysed him over the decades.
5. In 1985, Hawking was hospitalised with pneumonia and required an emergency tracheotomy, which caused permanent damage to his vocal cords and larynx. A keyboard-operated electronic speech synthesiser was adapted to fit his wheelchair by David Mason, an engineer married to Elaine Mason, one of Hawking's nurses.
6. He is known for his contributions to the fields of cosmology, general relativity and quantum gravity, particularly in the context of black holes. With English mathematical physicist Roger Penrose, Hawking showed that Einstein's General Theory of Relativity implied space and time would have a beginning in the Big Bang and an end in black holes.
7. Hawking's 1998 book A Brief History of Time became a bestseller and sold more than 10 million copies in 20 years. It was on the Sunday Times bestseller list for more than four years.
8. After 25 years of marriage and three children, Stephen and Jane Hawking – formerly Jane Wilde – separated and divorced in 1995. Stephen married his nurse, Elaine Mason.
9. Hawking and his daughter Lucy co-authored George's Secret Key to the Universe, a popular-science children's book published in 2007. It was followed by three sequels.
10. In 2009, Hawking was awarded the Presidential Medal of Freedom by President Barack Obama.