Gla'aki is a Great Old One, who first appeared in the 1964 novella The Inhabitant of the Lake, by Ramsey Campbell.
Gla'aki is presumed to have come to Earth imprisoned inside a meteor, which crashed somewhere in England, creating a lake in the Severn Valley near Brichester in England, where he still resides today.
Over time he gathered a cult, who wrote a 12 volume holy book in English called The Revelations of Gla'aki, which involved knowledge of Gla'aki, Y'golonac, Daoloth and other Great Old Ones & Outer Gods , as well as information of worship and sorcery.
Gla'aki resembles an enormous slug, covered with metal-like spikes that are actually organic. He can also extrude tentacles with eyes at the tips, giving him better eye-sight underwater.
- Gla'aki is a not a creation of Lovecraft himself, but a later addition by British writer Ramsey Campbell.