"Old One" is an ambiguous term in the Cthulhu Mythos, and may refer to:
- Great Old Ones, a pantheon of dead alien deities buried inside the Earth, including, Cthulhu. (The Call of Cthulhu).
- Outer Gods, a pantheon of deities who break inside the universe through Yog-Sothoth (The Dunwich Horror).
- Entities who can defeat the Deep Ones using a swastika symbol (The Shadow Over Innsmouth).
- Inhabitants of K'n-yan (The Mound).
- Elder Things, a species alien lifeforms (At the Mountains of Madness).