Immortal Thetis with the mortal Peleus in the foreground, Boeotian black-figure dish, c. 500–475 BC – Louvre.

Thetis (/ˈθɛtɪs/; Greek: Θέτις [tʰétis]), is encountered in Greek mythology mostly as a sea nymph or known as the goddess of water, one of the 50 Nereids, daughters of the ancient sea god Nereus. [ wikipedia entry ]