Chuck Clark is an American amateur astronomer and longtime watcher of the secret air base at Groom Lake, known as Area 51. For years he lived in a trailer in Rachel, Nevada, the tiny settlement on the Extraterrestrial Highway about 100 miles north of Las Vegas, and called himself a self-appointed military watchdog. He wrote the "Area 51 & S-4 Handbook," which was sold at the Little A'Le'Inn, Rachel's alien-themed restaurant and bar.

Clark told the Deseret News in 1996 that his interest dated to 1957, when he saw UFOs "playing cat and mouse with jet fighters" over Los Angeles. He also described seeing a craft whose maneuvers "defied the known laws of physics" at a time when he had no camera with him. In David Darlington's 1997 book on Area 51, Clark said that in February 1994 he had filmed, through a telescope, a sharp delta-shaped aircraft with twin tails taxiing from a lit Groom Lake hangar at 2:30 a.m., which he linked to the rumored Aurora spy plane. He said the tape was locked away.

His best-documented work concerned the base's perimeter. In 2003 Clark found a buried device marked as U.S. government property: a wireless transmitter wired to a roadside sensor that signaled when vehicles passed. With fellow watcher Joerg Arnu, he dug up 30 to 40 of the units on public land outside the boundary, logged their codes and positions, reburied them, and published the locations online. After he showed some to a KLAS-TV crew that June, FBI and Air Force agents searched his trailer and seized his computer, photographs and records. KLAS reporter George Knapp, writing in the Las Vegas Mercury, questioned how far the government could go to protect the base.

In December 2003 prosecutors charged Clark with one felony count of interfering with a national-defense communications system, alleging that a sensor had gone missing on March 12, 2003. Under a January 2004 agreement he accepted a year of pretrial diversion. In January 2005 the U.S. Attorney's Office in Las Vegas said he had paid for the missing sensor and met the conditions, and the case was dismissed. By 2004 he had largely stopped talking to the press.

Clark later became known as the keeper of a second tape, said to have been shot by other people and to show a UFO near the Nevada range, which he showed to a few visitors but would not release. Filmmaker James Fox spoke admiringly of it on a podcast, and in 2023 Logan Paul said he had offered $100,000 for it and secretly recorded a viewing with a button camera. That copy surfaced in April 2026 as the Chuck Clark UFO footage. Clark's place in Area 51 history rests on both: the hidden sensor network he exposed in 2003 and the tape he kept from public view for years.