From Arkham Horror Wiki
Flavor TextThe stench was unbearable, and rising to the surface came a terrible cry, "Tekeli-li! Tekeli-li!"
The origins of the shoggoths are fully detailed in the story At the Mountains of Madness (1931), written by H.P. Lovecraft. They are subsequently mentioned in The Shadow Over Innsmouth (1931) and The Thing on the Doorstep (1933).