The planet of the powerful Thasians, where the young Charlie Evans survived a crash alone and was given dangerous mental powers in the Original Series episode Charlie X.
Thasus is the world on which Charles Evans grew up, as told in the Original Series episode Charlie X. He was three years old when the transport carrying him crashed there, leaving him the only survivor. He was found fourteen years later by the survey ship Antares and claimed to have learned to talk from the wreck's memory banks.
The Thasians were believed to be a legend. In fact they are a non-corporeal people who gave the boy the power to change or destroy matter by thought, so that he could stay alive.
After Charlie destroys the Antares and terrorises the Enterprise, a Thasian ship arrives. Its commander restores what can be restored and takes Charlie back to Thasus, since his powers make him unable to live among humans.