William Henry Welch (April 8, 1850 – April 30, 1934) was an American physician, pathologist, bacteriologist, and medical school administrator. He was one of the "Big Four" founding professors at the Johns Hopkins Hospital. (The "Big Four", often called the "Four Horsemen", were William Osler, Professor of Medicine; William Stewart Halsted, Professor of Surgery; Howard A. Kelly, Professor of Gynecology; and William H. Welch, Professor of Pathology.) He was the first dean of the Johns Hopkins School of Medicine and was also the founder of the Johns Hopkins School of Hygiene and Public Health, the first school of public health in the country. The medical school library is also named after Welch. In his lifetime he was called "the Dean of American Medicine".