John Randolph Thune (born January 7, 1961) is an American politician serving as the senior United States senator from South Dakota, a seat he has held since 2005. Thune is in his fourth Senate term and is the Senate minority whip, a post he has held since 2021. A member of the Republican Party, Thune served three terms as the U.S. representative for South Dakota's at-large congressional district from 1997 to 2003.

Thune has worked in politics and civic organizations since completing his MBA degree. He is known for his defeat of sitting Senate Democratic Leader Tom Daschle in 2004. In the U.S. Senate, Thune served as the Republican chief deputy whip from 2007 to 2009 and chaired the Senate Republican Policy Committee from 2009 to 2012. He served as the Senate Republican Conference chair, the third-ranking position in the Senate, from 2012 to 2019.

The Senate Republican Conference selected Thune as majority whip for the 116th Congress; he succeeded Senator John Cornyn of Texas, who was term-limited in the position. In 2020, he was chosen as minority whip for the 117th Congress.