LINCOLN -- Historian David Herbert Donald was reading in his backyard one afternoon when he noticed two strangers -- a well-dressed, middle-aged couple -- standing just outside the fence.
''I got up and said, 'Is there anything I could do to help you?' " Donald, a two-time Pulitzer Prize winner, explained during a recent interview.
'' 'We are from Ohio,' " he quoted the woman as saying, '' 'And we are in New England on a tour of great American authors' homes. We just finished in Concord. We went to Emerson's house and Hawthorne's house and Alcott's house, and on our way back we thought we should stop in Lincoln and visit your house.' "
The 84-year-old scholar, mild in voice and manner, giggles self-consciously, tickled by the memory. Unless you're David McCullough or Stephen Ambrose, the historian's life is generally a private affair. But Donald is sought out by the known and the unknown, presidents and common readers. Fame, like a stranger in his yard, has come to him.
He has won Pulitzers for biographies of abolitionist Charles Sumner and novelist Thomas Wolfe, but his books on Abraham Lincoln are his true legacy. Presidents, from Kennedy to Bush, have summoned him for White House lectures and receptions. Many fellow scholars acknowledge him as the leader in the field. There's even an award named after him, the David Herbert Donald Prize for ''excellence in Lincoln studies." Last spring, Donald was the first honoree.
A professor emeritus at Harvard University, Donald has lived nearly 30 years in Lincoln, Mass., not in homage to the president, but because of good schools and easy access to Boston.
Donald plans to get off the Lincoln track and has started on a biography of an earlier president, John Quincy Adams, ''whose view on the way slavery could and would end was exactly Lincoln's view a generation later," he said.
The historian figures the Adams book will be ready in five years, when he's 89.