David Rice Atchison (August 11, 1807 – January 26, 1886) was an American Democratic politician. He was a United States Senator from Missouri. He was President pro tempore of the United States Senate for six years.
He is best known for the claim that for 24 hours—Sunday, March 4, 1849 through noon on Monday—he may have been Acting President of the United States. This, however, has been dismissed by nearly all historians, scholars, and biographers.