Arret was the homeworld of Sargon and his people.
The inhabitants of the planet ere engulfed in a devastating conflict that destroyed the surface of their world leaving only three survivors. (TOS episode: "Return to Tomorrow")
Settlers from the world were forced to abandon it due to the destruction brought about by their brethren. They were chosen to live on a new planet that was later designated as Gamma Trianguli VI millions of years ago before the world was encountered by Captain James T. Kirk. These inhabitants were only a small fraction of their race but vowed neve to allow the potential to destroy their newly adopted home as they did to Arret.
The supercomputer Vaal was built by the species that once inhabited this world. (TOS comic: "The Feeders of...Spock?")
In the antimatter universe, Arret is the planet of Karla Five and Karl Four. (TAS episode: "The Counter-Clock Incident")