Tethys was one of the Titans, daughter of Uranus and Gaea. She was married to her brother, Oceanus, and gave birth to the river gods, who lived in the rivers that were then known to the Greeks, such as the Nile and Alpheus; and to three thousand water goddesses, called Oceanids. Despite being the mother of so many deities in the Greek mythology, Tethys was not actively worshipped. During the Titanomachy, she raised Hera as her stepchild, brought to her by Rhea.
According to one myth, Hera did not like that Callisto and Arcas were placed in the heavens by being turned into the constellations Ursa Major and Ursa Minor, so she asked Tethys to do something about it. To appease Hera, Tethys denied the constellations from being able to touch the sea and fall below the horizon; instead, they were forever doomed to circle the sky.