Clarence William "Bill" Nelson II (born September 29, 1942) is an American politician and astronaut. Nelson is the 14th and current Administrator of the National Aeronautics and Space Administration since May 2021. He is a member of the Democratic Party. He was the United States Senator from Florida from 2001 to 2019. He lost his re-election campaign in 2018 to Republican Governor Rick Scott.
He was a member of the Florida House of Representatives from 1972 to 1978 and in the United States House of Representatives from 1979 to 1991. In January 1986, he became the second sitting member of Congress to fly in space, after Jake Garn. He was a payload specialist on the Space Shuttle Columbia.
Nelson retired from Congress in 1990 to run for Governor of Florida, but was lost the Democratic nomination to Lawton Chiles.
In March 2021, President Joe Biden nominated Nelson to be Administrator of the National Aeronautics and Space Administration in his administration.