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. Early life Born in South Boston, Massachusetts, he was the second of three sons of recent German immigrants, Charles Rudolph and Johanna Rockenbach. His elder brother, Rudolf Ernest Langer, became a mathematician and his younger brother, Walter Charles Langer, a psychoanalyst. When William was only three, his father died unexpectedly, leaving the family in difficult circumstances. Nevertheless, his mother, who supported the family by working as a dressmaker, made education a priority for her children. Education and career After studying at the Boston Latin School, Langer attended Harvard University. Langer was fluent in German, and taught German at Worcester Academy while furthering his own education with courses on international relations at Clark University. His job and education were interrupted by military service World War I. After the war, he returned to his studies and obtained his Ph.D. in 1923. In 1921 he married Susanne Katherina Langer (née Knauth) who became a noted philosopher. They had two sons together before divorcing in 1942. He taught modern European history at Clark University for four years before accepting an assistant professorship at Harvard. In 1936 Langer became the first to hold the Archibald Coolidge chair. Langer was remembered at Harvard especially for his History 132 course on modern European history, History 157 on the Ottoman Empire, and the graduate seminars held at his home. He also taught at the Harvard Extension School. With the help of other scholars during the 1930s, Langer completely revised the Epitome of History by German Scholar Karl Ploetz. Langer's massive work was published in 1940 under the title An Encyclopedia of World History. Its fifth edition (1972) is the last to be edited by Langer. Peter N. Stearns and thirty other prominent historians edited the sixth edition, published in 2001. Stearns paid tribute to Langer's great achievement in the introduction to the new edition. Later career In 1957, Langer urged historians to expand