Organians

The Organians were a race of powerful incorporeal beings composed of pure energy and thought in the Star Trek Universe.

Millions of years ago they existed as humanoids, but they evolved beyond the need for physical bodies.

For a period of ten thousand years, the Organians looked for indicators that observed corporeal species' intelligence was developed enough for first contact. They observed a planet that contained a silicon-based virus, and the reactions of species that encountered it, in an attempt to find a species with a higher level of intelligence. Among the species which the Organians observed attempting to deal with this deadly virus were the Klingons, Cardassians, and Humans. Thereafter contact was made with these species.

As beings of pure thought, they were either immortal or extremely long-lived. They also had the ability to occupy the bodies of humanoid hosts, as well as to alter or completely wipe their memories. They could be invisible when necessary and were aware of events at great distances.