During American medicine's "Heroic Age," when medical training and practice underwent revolutionary change, William Henry Welch emerged as a singular, revolutionary hero. The first full-time faculty member at the Johns Hopkins University School of Medicine, he became the undisputed leader of American scientific medicine and the greatest shaping force in American medical education. He won international fame as America's preeminent authority on medical issues—"our greatest statesman in the field of public health," in the words of Herbert Hoover—and earned the enduring affection of generations of colleagues and students as "Popsy", a brilliant, charming, and dedicated mentor.

William Henry Welch and the Heroic Age of American Medicine was originally published in 1941. By then Welch—who died in 1934 at age 84—was already a legend. He had founded the country's first pathological laboratory at the Bellevue Hospital Medical College. His "radical" innovations at the new Johns Hopkins School of Medicine had become the standard in American medical education: high entrance requirements, instruction in the laboratory, emphasis on basic science, and fostering of research. His vision had shaped a variety of other important institutions, including the Rockefeller Institute, the Association of American Physicians, Peking Union Medical College, and the country's first school of public health and hygiene, established at Johns Hopkins largely through his efforts. Welch's eightieth birthday had been celebrated nationally, with ceremonies in Washington, D.C., attended by President Hoover and broadcast around the world.