Mr. Burns, who taught at Williams College for most of the last half of the 20th century, was the author of more than 20 books, most notably “Roosevelt: The Soldier of Freedom” (1970), a major study of President Franklin D. Roosevelt’s stewardship of the country through World War II. It was awarded both the Pulitzer Prize and the National Book Award. Mr. Burns wrote “Leadership,” an amalgamation of a lifetime of thinking about the qualities shared and exemplified by world leaders throughout history. It became a standard academic text in the emerging discipline known as leadership studies, and Mr. Burns’s concept of transforming leadership itself became the subject of hundreds of doctoral theses. An informal adviser to presidents, Mr. Burns was a liberal Democrat who once ran for Congress from the westernmost district of Massachusetts. After graduating from Williams, Mr. Burns went to Washington and worked as a congressional aide. He served as an Army combat historian in the Pacific during World War II, receiving a Bronze Star, and afterward earned a Ph.D. from Harvard. He did postdoctoral work at the London School of Economics. The James MacGregor Burns Academy of Leadership was founded in 1997 at the University of Maryland. Mr. Burns’s two marriages ended in divorce. He is survived by three children and his companion, Susan Dunn, with whom he collaborated on “The Three Roosevelts” and a biography of George Washington, two of the half-dozen or so books Mr. Burns wrote or co-wrote after the age of 80.