Great Race of Yith

An "eternal" race of aliens was described by H. P. Lovecraft in The Shadow Out of Time. Befitting Lovecraft's nature as a Guardian of the Gate, they actually existed.

Their true physical forms were depicted in the book as "immense rugose cones ten feet high, and with head and other organs attached to foot-thick, distensible limbs spreading from the apexes. They spoke by the clicking or scraping of huge paws or claws attached to the end of their four limbs". However, they were most fearsome for their ability to project their minds through time and take over the bodies of other species. They were constantly at war, eager to expand their dominion and spawn more of their kind.

While working on his manuscript, Lovecraft found himself transported through time by a mysterious orb. During the journey, he caught glimpses of the actual aliens. Emerging in 2023, he warned Giles about them and gave him the manuscript before returning to his own time. (AUDIO: Guardian At The Gate)

Behind the scenes
These aliens, as described in the real-world version of, are the Great Race of Yith. They are never explicitly named in Guardian At The Gate. Meanwhile, the planet Yith was also mentioned in the Cwej: The Series short story The V Cwejes.