The story
Invented in 1926 by H.P. Lovecraft for his short story The Call of Cthulhu. Possibly based on chthonic (“dwelling under the earth”).
Etymology from Wiktionary, CC BY-SA 4.0.
Cthulhu
Today it means: A gigantic fictional humanoid alien god being described with a head resembling an octopus and dragon wings and claws, around whom an insane cult developed. Full definition →