Clarence William "Bill" Nelson II is an American politician and former shuttle crew member who represented Florida in Congress for three decades and served as the 14th administrator of NASA from May 2021 to January 2025. His place in the UAP record is institutional: during his tenure NASA commissioned its first study of unidentified anomalous phenomena, and he became the agency's public voice on the subject.

Born in Miami in 1942, Nelson studied at Yale and at the University of Virginia law school and served in the Army Reserve, including active duty from 1968 to 1970. He sat in the Florida House from 1972 to 1978 and in the U.S. House from 1979 to 1991. In January 1986, as a sitting congressman, he flew as a payload specialist aboard the space shuttle Columbia on mission STS-61-C. He represented Florida in the Senate from 2001 to 2019, losing his final race to Rick Scott after a recount. Confirmed as NASA administrator in April 2021, he was sworn in on May 3 and left office on January 20, 2025.

Nelson spoke about UAP early in his tenure. In an October 2021 University of Virginia livestream hosted by Larry Sabato, he said he had talked to the Navy pilots involved in the 2004 Nimitz encounter, that "their radars locked on to it," and that no one knew what they had seen. He said he hoped it was not an adversary's technology and asked who could say Earth was the only home of civilized life. In June 2022 NASA announced an independent team to examine how UAP could be studied scientifically; the 16-member panel held a public meeting in May 2023 and published its report that September.

Presenting the NASA UAP Independent Study report on September 14, 2023, Nelson said the team "did not find any evidence that UAP have an extra terrestrial origin, but we don't know what these UAP are." He announced a new NASA director of UAP research, later identified as Mark McInerney, and said his personal answer to whether life exists elsewhere in the universe was yes. Asked about the congressional testimony of David Grusch, he paraphrased Grusch's claims as things friends had told him and asked to see evidence; researcher Joe Murgia called the response an embarrassment.

Those remarks have been revisited since he left office. After the Department of War's 2026 UAP file releases, some disclosure commentators pointed to Apollo-era astronaut debriefings and lunar photographs in the files and argued that NASA under Nelson had been less forthcoming than he claimed, and podcasters contrasted his answers with those of his eventual successor, Jared Isaacman, confirmed in December 2025. Nelson's lasting mark on the subject is the study he authorized and the research post it created, the first time NASA formally treated UAP as a scientific data problem, framed throughout by his statement that the agency had found nothing pointing to an extraterrestrial origin.