Senator David Rice Atchison (1807-1886)
A proslavery Democrat, Atchison supported the Confederacy during the Civil War, participating in the 1856 sacking of Lawrence with Sheriff Sam Jones, and later riding with Quantrill in the Lawrence massacre.
A United States senator from Missouri (1843-55), David Rice Atchison is known to trivia buffs as the man who was "president for one day." Supporters claim he was president on 4 March 1849, when newly-elected president Zachary Taylor refused to take the oath of office on a Sunday. The term of incumbent James Polk ended that day at noon, leaving the office theoretically vacant until Taylor was sworn in on Monday.
As president pro tempore of the Senate, Atchison would presumably have been next in line for the job, but in actual practice Atchison was never sworn in or assigned the presidency in any way, and Taylor took the oath without incident on March 5th. As years passed, however, Atchison's "term" became a popular bit of historical lore, and his grave marker reads "David Rice Atchison -- President of the United States for One Day."
The town and county of Atchison, Kansas are named for him.