Unidentified: Inside America's UFO Investigation is a History Channel TV series purportedly exposing the US government's secret programs investigating unidentified flying objects (UFOs). It features former military counter-intelligence officer Luis Elizondo, who directed the Defense Intelligence Agency's Advanced Aerospace Threat Identification Program, and Christopher Mellon, former United States Deputy Assistant Secretary of Defense for Intelligence. Elizondo says that he resigned after he became frustrated that the government was not taking UFOs, which he considered to be a national security threat, seriously enough.