In 1931, the shy, brilliant British physicist Paul Dirac predicted the existence of a weird class of particles called antimatter. When Carl Anderson of Caltech quickly proved him right, Dirac should have become a household name, but his aversion to publicity—he almost turned down the Nobel Prize—discouraged media attention. Today he is known only among serious science fans, even though antimatter lies at the heart of some of the deepest mysteries in modern physics.