Tyro is the Aeolid princess of Elis who becomes queen of Iolcus — daughter of Salmoneus and Alcidice, wife of Cretheus, and by Poseidon (disguised as the river Enipeus) mother of the twins Pelias and Neleus. Through Cretheus she also bears Aeson, Pheres, and Amythaon, making her grandmother of Jason. Homer's Nekyia and Apollodorus preserve her river-loved story; the atlas keeps her distinct from later namesakes.
Adapted from Wikipedia, "Tyro" · CC BY-SA 4.0
I.Family
Tyro was daughter of King Salmoneus of Elis and Alcidice, daughter of Aleus of Arcadia. She married her uncle Cretheus, king of Iolcus, and bore him Aeson, Pheres, and Amythaon. By Poseidon she bore the twins Pelias and Neleus. Aeson became father of Jason of the Argonauts.
Some accounts add a daughter Phalanna, eponym of Phalanna in Thessaly. Hyginus and others also link her briefly to Sisyphus: fearing an oracle that children by that union would kill Salmoneus, she is said to have slain those offspring to spare her father.
II.Poseidon and the twins
Tyro loved the river-god Enipeus, who refused her. Poseidon, filled with desire, took Enipeus's form and lay with her; from that union came Pelias and Neleus. She exposed the twins on a mountain; a herdsman raised them. Grown, they found their mother and killed her stepmother Sidero for mistreating her — Pelias even slew Sidero in Hera's temple, earning the goddess's lasting hatred and, later, her patronage of Jason against Pelias.
Hesiod's Catalogue has Zeus rescue Tyro from Salmoneus's house and lead her to Cretheus; Homer's Odyssey already knows her as the river-loved mother of the Iolcan line.