Stephen Hawking is considered the world's foremost living theoretical physicist. He's an expert on black holes whose stated intention is to unify quantum mechanics with Einstein's general theory of relativity, forming a single theory to explain the origin (and end) of the universe. Hawking, a professor of mathematics at Cambridge University, is the author of the best-selling book A Brief History of Time and something of a celebrity: he has made guest appearances on the TV shows Star Trek and The Simpsons. Hawking has suffered from ALS (amyotrophic lateral sclerosis, also called Lou Gehrig's disease) since he was a young man and is confined to a wheelchair. He held the celebrated post of Lucasian Professor of Mathematics at Cambridge from 1979 until his retirement in 2009.