Stephen Hawking celebrates his 75th birthday

�In 2009, Hawking was awarded the Presidential Medal of Freedom by President Barack Obama.

Stephen Hawking celebrates his 75th birthday

Professor Stephen Hawking, on of the most prominent scientists of all time, turns 75 today.

He has continually defied medical odds after being diagnosed with amyotrophic lateral sclerosis (ALS) 50 years ago. Even today, Hawking still continues to carry out research, write and deliver lectures.

Hawking 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.

Stephen Hawking was born on 8 January 1942 in Oxford and grew up in St Albans. His father was a research biologist and his mother was a medical research secretary. In 1959, Hawking began his university education at University College, Oxford, at the age of 17.

He wanted to study mathematics, but it was not available at the university. So he went on to read physics instead, receiving a first class honours degree in natural science.

Hawking has 12 honorary degrees. He was awarded the CBE in 1982 and is a Fellow of The Royal Society and a Member of the US National Academy of Science.

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.

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.

His 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.

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.

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.