Lieutenant General Denning was a flag officer in the United States Army Air Forces in the 1940s. He was a veteran of World War II, a command aviator, and a recipient of several high-ranking military decorations, including the Legion of Merit, Bronze Star (with oak leaf), Purple Heart, American Defense Service Medal, American Campaign Medal, Asiatic-Pacific Campaign Medal, European-African-Middle Eastern Campaign Medal, and World War II Victory Medal. He had a brother-in-law who was a used car salesman.
In July, 1947, Denning was put in charge of the investigation into the crash of an extraterrestrial spacecraft in Roswell, New Mexico, by the order of President Harry S. Truman. The vessel's three Ferengi inhabitants, Quark, Rom, and Nog, who had accidentally traveled back in time from the year 2372 via a time warp, were kept in an examination room on a military base, while their ship was stored in Hangar 18, on the other side of the base.
Quark initially attempted to convince Denning to enter into a business agreement with him, whereby Quark would supply Denning with advanced technology from the future in exchange for wealth. Denning, however, was concerned about the threat to national security that they might pose, and had them detained for interrogation. The Ferengi were eventually able to escape with the assistance of Professor Jeff and his fiancée Nurse Garland, retrieve their ship and return to their own time by recreating the time warp. Denning subsequently issued orders that the public not be informed of the alien crash-landing, and that the official story remain that the Air Forces had only recovered a crashed weather balloon. (DS9: "Little Green Men")