Henry Steele Commager (October 25, 1902 – March 2, 1998) was an American historian who helped define Modern liberalism in the United States for two generations through his forty books and 700 essays and reviews. His principal scholarly works were his 1936 biography of Theodore Parker; his intellectual history The American Mind: An Interpretation of American Thought and Character since the 1880s (1950), which focuses on the evolution of liberalism in the American political mind from the 1880s to the 1940s; and his intellectual history Empire of Reason: How Europe Imagined and America Realized the Enlightenment (1977). In addition, he edited one of the most influential compilations of American historical documents, Documents of American History, which went through ten editions between 1938 and 1988 (the tenth, and last, coedited with Commager’s former student Milton Cantor.)
He won attention as one of the most active and prolific liberal intellectuals of his time, and he based his activism in support of the causes he advocated. In the 1940s and 1950s he was notable for his campaigns against the attacks and abuses of government power against liberals/the left wing—a political abuse known as McCarthyism. With his Columbia University colleague Allan Nevins, Commager helped to organize academic support for Adlai E. Stevenson and John F. Kennedy. Later in his career, he opposed the war in Vietnam, and was an articulate and energetic critic of Presidents Lyndon B. Johnson, Richard Nixon, and Ronald Reagan, and of what he purported was abuse of presidential power on each of their parts.