1. He is almost totally paralyzed, speechless and wheelchair-bound, able to move only his facial muscles and two fingers on his left hand. He cannot dress or feed himself, and he needs round-the-clock nursing care. He can communicate only through a voice synthesizer, which he operates by laboriously tapping out words on the computer attached to his motorized chair. Yet at age 50, despite these crushing adversities, Stephen Hawking has become, in the words of science writers Michael White and John Gribbin, "perhaps the greatest physicist of our time." His 1988 book, A Brief History of Time, has sold 1.7 million copies around the world.

2. Hawking's choice of career was most fortunate, for himself as well as for science. Rejecting the urging of his physician father to study medicine, Hawking chose instead to concentrate on math and theoretical physics, first at Oxford and then at Cambridge. But at age 21 he developed the first symptoms of amyotrophic lateral sclerosis (ALS), a disorder that would inevitably render him paralyzed and incapable of performing most kinds of work. Rs the authors note, theoretical physics was "one of the very few jobs for which his mind was the only real tool he needed."

3. He has used that tool with consummate skill. While still a graduate student, Hawking became fascinated by black holes, the bizarre objects created during the death throes of large stars. Working with mathematician Roger Penrose and using Einstein's relativity equations, he developed new techniques to prove mathematically that at the heart of black/holes were singularities—infinitely dense, dimensionless points with irresistible gravity. He went on to demonstrate that the entire universe could have sprung from a singularity and, in his 1966 Ph.D. thesis, wryly noted that "there is a singularity in our past."