Glaucus.
According to Ovid, Glaucus was a Boeotian fisherman who was changed into a sea deity by the gods after he ate a magical weed. He became a merman—half human, half fish. When the nymph Scylla spurned his advances, Glaucus asked the goddess Circe to use her powers to influence Scylla, but Circe herself loved the merman and refused. Glaucus rejected her, and Circe took vengeance on Scylla by poisoning the waters where she bathed with tainted herbs. Scylla was transformed into a monster whose lower body was covered with barking dogs; seeing her thus, Glaucus fled in fright. From her poisoned pool, Scylla waylaid Odysseus’s ship and killed six of his men. She was then changed into a rock on which unlucky ships were dashed to pieces.
       In the Odyssey, Homer describes the monstrous Scylla as having six heads, each with triple rows of teeth. In other tales, Glaucus was considered a patron of sailors and was renowned for his prophecies. He figures in some versions of the legend of the Argonautic expedition.

See also Circe; and Jason, and the Argonauts.