Leviathan

The Leviathan is the main antagonist of Call Of Cthulhu. It is a Star-Spawn worshipped by the inhabitants of Darkwater Island since the 14th century. It was mistaken for a giant whale and slain by the crew of the  Scylla, becoming known as the "Miraculous Catch". Consuming its eldritch flesh enabled it to curse the town's inhabitants from beyond death, gathering those who succumbed to its will into a cult dedicated to unleashing the Great Old One Cthulhu.