Mother Hydra.

Mother Hydra is a gigantic creature and alongside her consort Dagon is said to rule over the Lovecraftian race known as the Deep Ones .

There is debate as to whether or not Mother Hydra is a lesser Great Old One or merely a grotesquely mutated Deep One - though the latter seems more likely as she doesn't seem to show much in the way of supernatural power outside her gigantic size and unnaturally long life span.