The Greys are a post-species of cyborgs who have built a vast intergalactic civilization of planets which orbit around red dwarf stars. They are also the founders of the Greys' Galactic Network. Their large black eyes allow then to see on the planets that they have colonized which are dark and dim by standards of human eyes. No one knowns much about them. What is known is that they suppossedly evolved on an Earth-sized planet orbiting around a red dwarf star. And that the planet was spinning on its axis, unlike most planets orbiting around red dwarf stars, which are tidally locked at a distance from the red dwarf star that it orbits around. They have been known to abduct members of other species onboard their saucer ships and perform scientific experiments, just as they do with humans. They are also the species that crashed during the Roswell Incident.
Sub-Greys are species that are geneticly related to the Greys, but are different in other ways.