Like a lot of children, the six-year-old Stephen Jay Gould was fascinated by dinosaurs, but in his case that interest led to one of the most remarkable and celebrated careers in modern science. From his beginnings as a young paleontologist, with field expertise in the multifarious snails of the West Indies, he became a profound and influential evolutionary theorist. The principle of punctuated equilibrium he propounded is one of the most important contributions to our understanding of the origin of species since Charles Darwin first enunciated the theory of natural selection in the 1850s. An uncommonly entertaining speaker and writer, he illustrated scientific principles with colorful examples from his other lifelong passions: music, poker and baseball. Over 30 years of teaching at Harvard University, Gould used the full panoply of communications media to make the whole world his classroom. His magazine columns, television appearances and more than 20 books made him a leading spokesman for the theory of evolution and for science generally. On the public stage, he exposed the pseudo-science used to justify prejudice, and championed genuine scientific inquiry whenever it was threatened by religious orthodoxy. In his 60 years on earth, Stephen Jay Gould left a remarkable legacy of scholarship, creativity, and unwavering commitment to freedom of thought.