THX 1138 was George Lucas's first studio production after graduating from film school. It is an expanded version of Electronic Labyrinth: THX 1138 4EB, a prize winning student film. The film is set in a totalitarian society in which its citizens are forced to live underground and take drugs to suppress their emotions.
The central character, THX 1138, played by Robert Duvall, is tricked by LUH into not taking his pills, and together the two learn the emotion of real love. However, the totalitarian government discovers THX and LUH's transgression. THX is captured and incarcerated until he manages to escape with fellow prisoner SEN. After escaping, THX searches high and low for any sign of LUH, only to make the horrifying discovery that LUH had been murdered, as her name had been assigned to an unborn fetus.
With nothing else to lose and the authorities in pursuit, THX decides to take the only path left to him; escape from the underground city and climb to the surface. He manages to elude the robotic security forces, who are constantly monitored by a command center paying close attention to the amount of money being spent on the act of capturing THX. When he finds a ladder that will take him to the surface, he begins climbing. The security forces following him partially up the ladder until they're at last forced to turn back; the operation to catch THX had exceeded its allowed budget and had to be aborted.
Ignoring a security droid's final attempts to coerce him to return with them, THX climbs to the top of the ladder and escapes through a hatch. The film ends with him standing against a brilliant sunset, a free man at the cost of everyone and everything he had ever known.
George Lucas has fit small references to THX 1138 in all of his subsequent films. For example, in Star Wars, Princess Leia is held in cell block 1138, while a car in American Graffiti has the license plate THX 138.