Oscar Wilder Underwood (May 6, 1862-January 25, 1929) was an American politician. He served as a Representative from Alabama in the House of Representatives from 1895 to 1896 and from 1897 to 1915. He was subsequently elected to the Senate and served there from March 4, 1915 to March 3, 1927, and did not run for reelection in 1926.
Underwood was the first House minority whip from 1900 to 1901. He was then House majority leader between 1911 and 1915. Finally, he was Senate minority leader from 1920 to 1923. He was a candidate for the Democratic vice presidential nomination in 1912 and the Democratic presidential nomination in 1924. He was a "wet" (opponent of prohibition), and was the leader of the anti-Ku Klux Klan forces in the Democratic party in 1924.