David Atchison was an American politician and lawyer who served as a U.S. Senator from Missouri from 1843 to 1855. He is best known for his brief tenure as President of the United States, albeit unofficially, for one day in 1849. Atchison was the President pro tempore of the Senate at the time, and due to the absence of both the President and Vice President, he claimed the role for a single day. Atchison was a prominent supporter of the Democratic Party and was involved in the contentious issues surrounding slavery and westward expansion. He played a significant role in the Kansas-Nebraska Act, which allowed territories to decide on the legality of slavery. His political career was marked by his advocacy for pro-slavery policies during a turbulent period in American history.