*** FILE *** British mathematician, astrophysicist (cosmologist) Stephen W. Hawking smiles during a news conference at the University of Potsdam, near Berlin, Germany, in this Wednesday, July 21, 1999 file photo. Cambridge University confirmed on Friday Oct. 24, 2008 that Hawking would retire as Lucasian Professor of Mathematics, a title once held by Isaac Newton, at the end of the academic year in September. He will take the title of Emeritus Lucasian Professor of Mathematics. University policy is that officeholders must retire at the end of the academic year in which they become 67. Hawking will reach that milestone on Jan. 8. (AP Photo/Markus Schreiber, FILE)
Cambridge University said the 67-year-old is "comfortable" and will stay overnight at Addenbrookes Hospital in Cambridge. Hawking, one of the world's most famous physicists, is also a cosmologist, astronomer, and mathematician.
Wheelchair-bound Hawking is perhaps most famous for "A Brief History of Time" which explored the origins of the universe in layman's terms, is considered a modern classic. Hawking has Lou Gehrig's Disease (Amyotrophic Lateral Sclerosis, or ALS), which is usually fatal after three years. Hawking has survived for more than 40 years since his diagnosis.
On his Web site, Hawking has written about living with ALS. "I try to lead as normal a life as possible, and not think about my condition, or regret the things it prevents me from doing, which are not that many," he wrote.
He added: "I have been lucky, that my condition has progressed more slowly than is often the case. But it shows that one need not lose hope."
The disease has left him paralyzed -- he is able to move only a few fingers on one hand. Hawking is completely dependent on others or technology for virtually everything -- bathing, dressing, eating, even speech. He uses a speech synthesizer with an American accent. Watch Larry King's interview with Hawking in 1999 »
Hawking has been married and divorced twice. In 2004, police completed an investigation into accusations by Hawking's daughter that his second wife was abusing him. Authorities said they found no proof.
A Cambridge University spokesman told CNN: "Professor Hawking is very ill and has been taken by ambulance to Addenbrookes Hospital, Cambridge."
Professor Peter Haynes, head of the university's department of Applied Mathematics and Theoretical Physics, said: "Professor Hawking is a remarkable colleague, we all hope he will be amongst us again soon."
At Cambridge, he holds the position of Lucasian Professor Mathematics -- the prestigious post held from 1669 to 1702 by Sir Isaac Newton.
In October, CNN's Becky Anderson interviewed Hawking. The following are some quotes from that interview:
"Over the last twenty years, observations have to a large extent confirmed the picture I painted in 'A Brief History of Time.' The one major development that was not anticipated was the discovery that the expansion of the universe is accelerating now, rather than slowing down... We live in the most probable of all possible worlds."