FO is a 1970 British television science fiction series about an alien invasion of Earth, created by Gerry Anderson and Sylvia Anderson with Reg Hill, and produced by the Andersons and Lew Grade's Century 21 Productions for Grade's ITC Entertainment company.
UFO first aired in the UK and Canada in 1970 and in US syndication over the next two years. In all, 26 episodes, including the pilot, were filmed over the course of more than a year, with a five-month production break caused by the closure of the MGM-British Studios in Borehamwood, where the show was initially made.
The Andersons had previously made a number of very successful children's science fiction series using marionettes, including Supercar, Fireball XL5, Stingray, Thunderbirds, and Captain Scarlet and the Mysterons. They had also made one live-action science fiction movie, Doppelgänger, also known as Journey to the Far Side of the Sun, and now felt ready to move into live-action television and aim at a more adult market.
UFO was the Andersons' first totally live-action TV series. Despite the assumption of many TV station executives, the series was not aimed at children but was intended for an older audience; many episodes featured adult themes such as adultery, divorce, and drug use. Most of the cast were newcomers to Century 21 although star Ed Bishop had previously worked with the Andersons as a voice actor on Captain Scarlet and The Mysterons.Overview from themoviedb.org