Organian

The Organians are non-corporeal life forms native to the planet Organia.

The Organians were at one time corporeal life-forms, but transcended their material bodies 22 million years ago. (LUG RPG: All Our Yesterdays.)

By 2154, the Organians had already made extensive studies of various species when they made first contact with humans via the crew of the Enterprise. The Organians erased all memory of their existence from the crew's minds, but began preparations for an official first contact. (ENT episode: "Observer Effect")

In 2267, when war broke out between the Federation and the Klingon Empire, the Enterprise attempted to secure Organia, but the planet was invaded by a Klingon task force led by Commander Kor. The war was ended when the Organians forced both sides to sign the Organian Peace Treaty. (TOS episode: "Errand of Mercy").

In 2269, the Klingons confined the Organians to their planet with a "thought-barrier", thus allowing war to break out between the Federation and Klingons once again. After the Enterprise reached Organia and freed it, the Organians confined the Klingons to their homeworld for 1000 years.* (TOS novel: Spock Must Die!)


 * * This in obvious contradiction with later incarnations of Star Trek.

The Organians temporarily left the material plane (perhaps by choice) in the year 2285, after apparently being manipulated by natives of the planet Excalbia. This resulted in the disolution of The Organian Peace Treaty and allowed the Federation and Klingon powers to forge a peace on their own terms. (TOS DC comic first series issues 3-4 Errand of War; Deadly Allies)

In 2371, as James T. Kirk lay near death on Veridian III, he was revisited by the leaders of Organia, who showed him the difference his decisions made in history. (TOS short story: "Reflections")