Roger Krevin Leir was an American podiatric surgeon and ufologist, born in San Francisco in 1935, who became the best-known investigator of alleged alien implants. For nearly two decades he removed small foreign bodies from patients who reported abduction experiences and argued that some of them were manufactured devices placed by non-human beings. The claim made him a fixture of abduction books, UFO conferences and late-night radio from the late 1990s until his passing in 2014.

Leir moved to southern California at 13, earned a bachelor's degree in science from the University of Southern California in 1961 and qualified as a podiatrist in 1964. He practiced in Ventura County and became active in the local chapter of the Mutual UFO Network. His turn toward implants came at a 1995 MUFON conference, where he examined X-rays from a woman who believed she had been abducted; he later removed small metallic objects from her and from a second patient. The New Mexico Institute of Mining and Technology reported that the fragments were composed of commonly found elements, but Leir concluded they were of extraterrestrial origin.

He set out that case in The Aliens and the Scalpel (1998) and followed it with Casebook: Alien Implants (2000). Working with a dentist, a radiologist, a general surgeon and materials scientist Steve Colbern, who analyzed specimens for him, Leir described objects he said emitted radio signals, responded to magnetism or showed unusual crystalline structures. In 2003 he traveled to Brazil to research the 1996 Varginha case, the subject of his 2005 book UFO Crash in Brazil, and he discussed both subjects as a frequent guest on Coast to Coast AM.

Skeptical investigator Joe Nickell argued that the objects were most likely ordinary debris, such as shards of glass or metal that become lodged in feet and legs through falls or barefoot walking, and said that Leir did not share his data or specimens with outside researchers. Admirers, including author Whitley Strieber, called him a pioneer, and in 2012 MUFON chapters in Los Angeles and Orange County held tribute meetings to help with his medical bills. His last surgery, on a man who reported hostile childhood encounters, was filmed by Jeremy Corbell for the 2017 documentary Patient Seventeen; laboratory tests on the removed fragment were reported as inconclusive. Leir passed away in Thousand Oaks, California, in March 2014.

His specimens and stories have outlived him. Colbern continued to analyze and discuss the Leir implants, abduction researcher Steve Aspin cited the removals in 2026 interviews about physical traces of abduction, and in October 2026 researcher Joe Murgia noted that an account attributed to an alleged legacy-program insider resembled a Varginha story Leir told Art Bell in 2004. No implant from his surgeries has been independently shown to be non-human technology, yet Leir remains the surgeon most closely identified with the idea that abductees carry physical devices, and his case files are still the starting point for anyone pursuing that claim.