In Greek mythology, Tethys is one of the Titans, daughter of Uranus and Gaia, sister-wife of Oceanus, and mother of the river gods and the Oceanids. She has almost no independent narrative cult, yet Homer makes her Hera's foster mother, and later mosaics of the Greek East repeatedly portray her as a sea goddess. This entry is the Titaness — not Saturn's moon Tethys, the prehistoric Tethys Ocean, or the Nereid Thetis.
Adapted from Wikipedia, "Tethys (mythology)" · CC BY-SA 4.0
I.Family and primeval mother
Hesiod counts Tethys among the Titans and makes her the wife of Oceanus. Together they produce innumerable river gods and Oceanids — the watery kin that populate later myth as mothers of heroes, consorts of gods, and personified streams.
In the Iliad's Deception of Zeus, Hera twice names "Oceanus, from whom the gods are sprung, and mother Tethys," and recalls being nursed in their halls while Zeus overthrew Cronus. Plato and Orphic-leaning genealogies sometimes place Oceanus and Tethys as parents of the other Titans, reconciling Homeric and Hesiodic schemes.
II.Few myths
Beyond fostering Hera, early story almost ignores Tethys. Hera's Iliadic ruse claims she is travelling to reconcile Oceanus and Tethys, who have quarrelled and ceased their embraces. A later astral tale forbids Callisto (as Ursa Major) from setting into Ocean because Tethys, out of regard for foster-child Hera, bars Zeus's former lover from the waters. Claudian has her nurse the infant Helios and Selene; Ovid has her transform Aesacus into a diving bird.
Hellenistic and Roman poets often use "Tethys" as a metonym for the sea. She is frequently confused in modern discussion with Thetis, the Nereid mother of Achilles — a different goddess.
III.Iconography and namesakes
Archaic vase-painting shows her (inscribed) following Oceanus at the wedding of Peleus and Thetis. From the second to fourth centuries CE she appears often in eastern mosaics — alone or with Oceanus — in baths and dining rooms, identified by forehead wings, a rudder, and a ketos. Late examples blur toward Thalassa, the personified sea.
Saturn's moon Tethys and the geological Tethys Ocean borrow her name. This encyclopedic notice concerns only the Titaness consort of Oceanus.