Landru was a mytho-historical leader of the Beta III natives.
In approximately 4000 BC, war threatened to destroy the planet Beta III and its inhabitants. The leader at that time was a gifted engineer and philosopher, Landru. He believed the way to preserve his people was to take them back to a time of peace and tranquility. He sought to end war, crime, disease – all of the evils that plagued his world, and to produce "the unity of good" – a world without hate, without fear, without conflict. To that end, he built and programmed a sophisticated machine, which took on his identity. (TOS: "The Return of the Archons")
In "The Return of the Archons, Part 2", an issue of IDW's Star Trek: Ongoing comic series, it was revealed that Landru (first name Cornelius (β)) was the head of Starfleet's Advanced Research Division and was apparently creating an artificial intelligence to assist in colony development. His true intentions were more sinister: he was attempting a means of population control. The crew of the Archon attempted to stop him, but the ship was destroyed: the ship's crashed remains were built into a temple by the descendants of the crew's survivors. After the computer was removed, Admiral Pike was admonished by an unseen superior for not keeping a tighter leash on his protege Kirk after exposing the secret experiment that lasted for decades.