Who was the only U.S. President to never marry?

As of 2014, the only U.S. president never to marry was James Buchanan. His niece, Harriet Lane, served as First Lady, acting as White House hostess during a turbulent time in history.

James Buchanan was the 15th president, serving only one term from 1857 to 1861. Though he was a lifelong bachelor, he became Harriet's guardian when she was only 11 years old. He had been very active in government affairs for years before running for president but came into office just as the nation's divisiveness over slavery was reaching its height. Despite his efforts to keep the nation together, seven states seceded from the Union under his presidency.