The cause of death was unclear, but Gienapp was known to be suffering from cancer, and had recently taken at least one leave of absence.
“He was a wonderful man, a wonderful historian and a great teacher,” Winthrop Professor of History Stephan Thernstrom said.
Gienapp’s scholarship focused on the Civil War and Reconstruction. His books included his 1988 work, The Origins of the Republican Party, 1852-1856, as well as Abraham Lincoln and Civil War America: A Biography, published in 2002.
Gienapp’s colleagues praised his skill as a teacher and remembered him for his popularity among students.
“He had a real following among students,” Dunwalke Associate Professor of American History Sven Beckert said. “He always had time for you.”
Dean of the Faculty William C. Kirby, who taught in the history department prior to assuming the deanship, called Gienapp “one of the great teachers of this Faculty.”
“He was a simply outstanding lecturer, in the best Harvard tradition.... He was a man of exacting standards, for himself, for his students, and for his profession. I will miss him terribly,” Kirby wrote in an e-mail.
Students also spoke highly of Gienapp.
Raymond C. Hohenstein II ’04-’05, who took History 1653, “Baseball and American Society, 1840-Present,” said that Gienapp would wear a cap each day from the era they were discussing in class.
“People came to hear him lecture,” he said. “The lecture hall was packed for every single class.”
Elisabeth L. Laskin, a lecturer in the history department who studied under Gienapp, said he arranged department trips to Red Sox games.
Gienapp’s lecture rooms were regularly packed full of undergraduates, who clamored to get into such courses as Historical Study B-42, “The American Civil War, 1861-1865” and History 1644, “Reconstruction, 1865-1877.”
Gienapp assumed a permanent post at Harvard in 1989.
Previously to that he served on the faculty at the University of Wyoming and as a visiting associate professor at Harvard.
Colleagues and students in the History department said that despite his illness, Gienapp’s death came as a surprise.
“He had been terribly ill for a long time, but he seemed to be recovering,” Thernstrom said.
—Staff writer Yailett Fernandez can be reached at firstname.lastname@example.org.