The Thasians were a race of non-corporeal beings with extremely powerful psychokinetic abilities, native to the planet Thasus. Once believed to be only a myth, Thasians were finally encountered by the USS Enterprise in 2266.
In 2252, a ship crashed on Thasus, with a young boy, Charles Evans, the only survivor. The Thasians found Charlie and granted him their psychokinetic powers so that he could survive. In 2266, Charlie was rescued from Thasus and transferred aboard the Enterprise from the survey vessel Antares for transportation to Colony 5, where he could be reunited with his closest living relatives.
The Thasians did not realize Charlie was gone until it was too late, however. Charlie's great psychokinetic powers, combined with his immaturity and petulance, made him a great threat to others he encountered. He took control of the Enterprise and even destroyed the Antares before the Thasians could intervene. Eventually, the Thasians did arrive, and were able to reverse all of the changes Charlie made aboard the Enterprise, but were unable to save the Antares. Taking on his form of centuries previous, before the Thasians had evolved beyond the need for physical bodies, a Thasian appeared on the Enterprise bridge as a translucent, floating humanoid head. He apologized to the crew of the Enterprise for the havoc Charlie had wrought on board, and for the destruction of the Antares, explaining that they had arrived to retrieve Charlie. When Captain Kirk asserted that Charlie should remain amongst his own kind, the Thasian countered by stating that Charlie was too much of a danger, and that he could never be taught to cease the use of his powers. Reluctantly agreeing, Captain Kirk allowed the Thasians to take Charlie back to Thasus, despite Charlie's protestations. (TOS: "Charlie X")