Tethys is a sea Titanide and a daughter of Uranus and Gaia. She personifies the underground rivers and springs. She is married to the ancient sea Titan, Oceanus.

Tethys and Oceanus raised many children together, numbering in the multiple thousands. The Oceanids alone already include around 3000 children, all protectors of the oceans. Their other children protect the rivers. These are the Potamids and Nyads.

Tethys is closely associated with childcare and nursing. Indeed, she is the foster mother of none other than Hera. And when Helios and Selene needed a wetnurse, Thetys nursed them to full strength. She is not to be confused with Tethis, who is the mother of Achilles. She is a different individual altogether.