Known primarily as a Lincoln historian, he also won Pulitzer Prizes for his biographies of abolitionist Charles Sumner and novelist Thomas Wolfe. His famous biography of Abraham Lincoln was published in 1995.
He studied sociology and history at Mississippi's Millsaps College. He later received his PhD from the University of Illinois, where he studied with the renowned Lincoln scholar, James G. Randall.
He was unsentimental in writing about Lincoln, portraying him as a keen manipulator of the political machine.
He grew up in Goodman, Mississippi, where his father worked as a farmer and his mother taught grade school. He died in Boston, Massachusetts and was survived by his wife and three children.
At the time of his death, he was working on a volume about John Quincy Adams.