Edward Jenner is a giant of modern medicine. Throughout history, smallpox plagued humanity as an incurable blight, the suffering of which Jenner helped bring to an end. Surmising from milkmaids' immunity that cowpox might defend against smallpox, in 1793 he inserted some of the matter from a human case of cowpox into a boy's arms. He subsequently inoculated the boy with smallpox itself, and found him to be immune. In 1979 smallpox was declared extinct. This is the story of Jenner’s life and his profound legacy of medical experimentation, public health provision, and the prevention of other diseases, from anthrax to measles.