William Leonard Langer (March 16, 1896 – December 26, 1977) was an American historian, intelligence analyst and policy advisor. He served as chairman of the history department at Harvard University. He was on leave during World War II as head of the Research and Analysis Branch of the Office of Strategic Services. He was a specialist on the diplomacy of the periods 1840–1900 and World War II. He edited many books, including a series on European history, a large-scale reference book, and a university textbook. Source: Wikipedia (en)