Thetis is one of the 50 Nereids (sea nymphs) and a sea goddess in Greek mythology. Thetis is best known for being the mother of the Greek hero Achilles; however, her role goes beyond that; appears in several stories and interacts with multiple gods and goddesses, often caring for gods and heroes in need.

Described as blonde and silver-footed, Thetis was the most prominent of the Nereids (along with Amphitrite), with the power to transform into different forms. Her wedding to King Peleus was the most splendid in Greek mythology and was part of the catalyst for the Trojan War.

According to Hesiod (c. 700 BC) in his Theogony, Thetis was one of the 50 beautiful Nereids born to Nereus, the Old Man of the Sea, and Doris (a sea goddess).

Nereids were beautiful sea nymphs who personified their specific elements. They lived at the bottom of the sea in caverns and sat on golden thrones. They glided through the water and danced on the banks. The Nereids were part of Poseidon’s underwater royal procession, along with other sea deities and creatures.