KIMONIANS

Planet of Origin: Kimon, an earth-type planet orbiting a yellow star in the milky way galaxy.
Kimonians are a seemingly humanoid species looking much like a perfect if a bit taller version of humanity. They possess powerful psionic abilities such as telepathy, telekynesis - which is the basis of their craft- and teleportation with a range that allows them to send objects over interstellar distances. They also have the power to help individuals of some other species to develop psionic powers of their own.
They have developped a peaceful non-expansive pastorale advanced civilisation on their homeworld and have shown no interest in other worlds and other civilisations although they are known to accept humans of Earth among them providing they have a high IQ and succeed a very severe series of tests.
It remains unknown if the form under which we see them is their real appearance as they are known to influence perceptions of off-worlders on a regular basis.
Source: Immigrant, by Clifford Donald Simak