A planet whose society is run by the ancient computer Landru, where the USS Archon disappeared a century before Kirk's visit.
Beta III in star system C-111 is a world whose people live in a placid, controlled society reminiscent of nineteenth-century Earth. Their lives are governed by Landru, a computer built by a long-dead leader of the same name to preserve order after a time of war. Those who resist are absorbed into the Body, while periodic violent Festivals release the population's suppressed energy.
In The Return of the Archons, Kirk comes to Beta III to discover what happened to the USS Archon, which vanished there a hundred years earlier. With help from the underground, he finds Landru and persuades it that it is harming the people it was built to protect.