Thetis is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, and one of the 50 Nereids, daughters of the ancient sea god Nereus.
Immortal Thetis with the mortal Peleus in the foreground, Boeotian black-figure dish, c. 500–475 BC - Louvre
Thetis changing into a lioness as she is attacked by Peleus, Attic red-figured kylix by Douris, c. 490 BC from Vulci, Etruria - Bibliothèque nationale de France in Paris
Thetis dips Achilles in the Styx by Peter Paul Rubens (between 1630 and 1635)
In Greek mythology, Achilles or Achilleus was a hero of the Trojan War who was known as being the greatest of all the Greek warriors. A central character in Homer's Iliad, he was the son of the Nereid Thetis and Peleus, king of Phthia and famous Argonaut. Achilles was raised in Phthia along with his childhood companion Patroclus and received his education by the centaur Chiron. In the Iliad, he is presented as the commander of the mythical tribe of the Myrmidons.
The Education of Achilles, by Eugène Delacroix, pastel on paper, c. 1862 (Getty Center, Los Angeles)
The Education of Achilles (c. 1772), by James Barry (Yale Center for British Art)