Up to 2016, who was the only US President to remain a life long bachelor?

James Buchanan, Jr. (/bjuːˈkænən/; April 23, 1791 – June 1, 1868) was the 15th President of the United States (1857–61), serving immediately prior to the American Civil War. He represented Pennsylvania in the United States House of Representatives and later the Senate, then served as Minister to Russia under President Andrew Jackson. He was named Secretary of State under President James K. Polk, and as of 2016 is the last former Secretary of State to serve as President of the United States. After Buchanan turned down an offer to sit on the Supreme Court, President Franklin Pierce appointed him Ambassador to the United Kingdom, in which capacity he helped draft the Ostend Manifesto.

He is, to date, the only president from Pennsylvania and the only president to remain a lifelong bachelor. He was the last president born in the 18th century.