According to one account, the world was inhabited by the a small faction of settlers from the planet Arret who, after seeing the devastation wrought on their world, decided to prevent the potential of happening to their newly adopted home. To accomplish this, they stored their collective knowledge within the supercomputer known as Vaal which wiped the memories of the settlers past. The computer was then charged with guiding the inhabitants while ensuring that they never advanced to the state where they could threaten to destroy the world itself.
Another chronological estimate maintains that the Vaalians were originally placed on the planet by members of Sargon's race millions (not tens of thousands) of years earlier, with the Vaal computer-entity being tasked with a similar purpose. Despite appearing as a stable living planet, Gamma Trianguli VI was a synthetic world that was held together by Vaal. Without the guidance of the computer, the planet would have self destructed. (TOS comic: "Devil Down Below!")