Thetis (; ), is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, or one of the 50 Nereids, daughters of the ancient sea god Nereus. When described as a Nereid in Classical myths, Thetis was the daughter of Nereus and Doris, and a granddaughter of Tethys with whom she sometimes shares characteristics. Often she seems to lead the Nereids as they attend to her tasks. Sometimes she also is identified with Metis. Some sources argue that she was one of the earliest of deities worshipped in Archaic Greece, the oral traditions and records of which are lost. Only one written record, a fragment, exists attesting to her worship and an early Alcman hymn exists that identifies Thetis as the creator of the universe. Worship of Thetis as the goddess is documented to have persisted in some regions by historical writers such as Pausanias. In the Trojan War cycle of myth, the wedding of Thetis and the Greek hero Peleus is one of the precipitating events in the war which also led to the birth of their child Achilles. As a goddess Most extant material about Thetis concerns her role as mother of Achilles, but there is some evidence that as the sea-goddess she played a more central role in the religious beliefs and practices of Archaic Greece. The pre-modern etymology of her name, from tithemi (τίθημι), "to set up, establish," suggests a perception among Classical Greeks of an early political role. Walter Burkert considers her name a transformed doublet of Tethys. In Iliad I, Achilles recalls to his mother her role in defending, and thus legitimizing, the reign of Zeus against an incipient rebellion by three Olympians, each of whom has pre-Olympian roots: You alone of all the gods saved Zeus the Darkener of the Skies from an inglorious fate, when some of the other Olympians – Hera, Poseidon, and Pallas Athene – had plotted to throw him into chains ... You, goddess, went and saved him from that indignity. You quickly summoned to high Olympus the monster of the hundred arms whom the gods call Briareus, but mankind Aegaeon, a giant more powerful even than his father. He squatted by the Son of Cronos with such a show of force that the blessed gods slunk off in terror, leaving Zeus free — E.V. Rieu translation Quintus of