SAUL TEUKOLSKY is the Hans A. Bethe Professor of Physics and Astrophysics at Cornell University and the Robinson Professor of Theoretical Astrophysics at Caltech. Among his many honors, he is a member of the National Academy of Sciences and the American Academy of Arts and Sciences. A native of South Africa, he first became fascinated by Einstein when he was in high school, and wanted to understand what all the fuss was about. The many popular books on relativity he read really didn’t do it for him, so he resorted to reading textbooks on his own. He finally understood what relativity was about as a graduate student of Kip Thorne at Caltech. But by then he was ill-­equipped to do much of anything else, so he had to become a researcher in the field. He soon discovered that many problems he wanted to solve could not be solved by traditional pencil-­and-paper mathematics, so he needed to learn about supercomputers to tackle these problems. One consequence of this was that he ended up co-­authoring a book on the subject of computation, Numerical Recipes: The Art of Scientific Computing — a bestseller, which has been widely read and used in classrooms the world over.