One of the Great Old Ones featured in Cthulhu Mythos fictions. Glaaki resides primarily in a Severn Valley lake near Brichester in England. Glaaki first appeared in The Inhabitant of the Lake , an early story by Ramsey Campbell.

Glaaki has the appearance of an enormous slug, covered with spines. Despite being metal, these spines have a cellular structure, showing them to be organic growths. It is also able to extrude tentacles with eyes at the tips, allowing it to see out of the water it resides in.

Glaaki is served by a cult, to which it has given sorcerous knowledge in the form of the twelve-volume Revelations of Glaaki. Many people come to serve Glaaki willingly, in exchange for the promise of eternal life. What they don't realise is that it makes good on its promise by driving one of its spines into them, allowing the venom it contains to transform them into a mindless, undead servant of Glaaki .