Cetus or Ketus, in Greek Mythology, is a primordial marine deity daughter of Pontos, the Sea, and Gaia, the Earth. The name Cetus, which means "monster", is how the ancient Greeks called whales, which for them were sea monsters. Ceto is the personification of the dangers of the sea. She was more specifically a goddess of whales, sharks and sea monsters. Also considered a goddess of horrors and strange, colorful and exuberant forms that the sea can produce and reveal to men. Sister and wife of Fórcis, the goddess receives these epithets: Krataiis (Κράταιις, "powerful, of the rocks"); Lamía (Λαμία, "the shark"); Triennes (Τρίενος, "within three years").
Its symbols are whales; sharks; big fish and the sea. According to Hesiod, in his Theogony, Ceto was an extremely beautiful goddess who begat beautiful but dangerous daughters and hated by the gods. However, as is common to marine deities, Ceto has a dual aspect: while she was considered to have divine beauty, they were also seen with an abyssal monster capable of generating other monsters like herself: the Gorgons, the Greias and the sleepless Dragon Ladão . Echidna, also his daughter, was an ambiguous creature, with the trunk of a beautiful nymph and a snake's tail instead of the limbs.