He was Poseidon's son or Anthedon's or Polyvos' or Phorvos' or Nereus'. He was a fisherman and an excellent swimmer as well as an excellent shipbuilder. He wedded Symi and dwelt on a desert island , opposite Caria of Minor Asia, to which he gave his wife's name. The legend declares that once as he was carrying some fish he had caught, he got tired and put the load down on the ground so that he could have some rest. Then one of the fish as soon as it ate some kind of herbs, which were around, jumped into the sea again. Glaucus, thinking that it was that herb which put new life to the fish, tasted the herb himself and immediately he went "mad" and jumped into the sea as well. Poseidon and the other sea-deities received him favourably and made him immortal, too.

According to Diodorus, when the Argonauts were on their way back to Iolkos, in the middle of the Euxinus Pontus, they fell into heavy seas and risked their lives. Orpheas then prayed to the gods of Samothraki and when at last the winds started to abate, Glaucus emerged out of the sea before them. After he had foretold what was going to happen to each Argonaut he advised them as soon as they set foot on land, they should pray to gods and thank them.