John A. Keel's 1970 work, Operation Trojan Horse: The Classic Breakthrough Study of UFOs , challenges the extraterrestrial hypothesis by proposing that UFO phenomena are "ultraterrestrial" manifestations, or deceptive, non-human entities. The book links modern UFO sightings to historical folklore, suggesting these apparitions act as a form of manipulation or "hostile deception". Find detailed information and summaries on Wikipedia .