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.

After Achilles's death, Thetis does not need to appeal to Zeus for immortality for her son, as the two have an established rapport (due to Thetis helping him in a dispute with three other Olympians) and snatches him away to the White Island Leuke in the Black Sea, an alternate Elysium,[5] where he has transcended death, and where an Achilles cult lingered into historical times.

Pseudo-Apollodorus' Bibliotheke asserts that Thetis was courted by both Zeus and Poseidon, but she was married off to the mortal Peleus because of their fears about the prophecy by Themis[6] (or Prometheus, or Calchas, according to others) that her son would become greater than his father.

(Slatkin 1986:12) When Hephaestus was thrown from Olympus, whether cast out by Hera for his lameness or evicted by Zeus for taking Hera's side, the Oceanid Eurynome and the Nereid Thetis caught him and allowed him to stay on the volcanic isle of Lemnos, while he labored for them as a smith, "working there in the hollow of the cave, and the stream of Okeanos around us went on forever with its foam and its murmur" (Iliad 18.369).

Diomedes recalls that when Dionysus was expelled by Lycurgus with the Olympians' aid, he took refuge in the Erythraean Sea with Thetis in a bed of seaweed (6.123ff).

Where within the framework of the Iliad the ultimate recourse is to Zeus for protection, here the poem seems to point to an alternative structure of cosmic relations.

In order to ensure a mortal father for her eventual offspring, Zeus and his brother Poseidon made arrangements for her to marry a human, Peleus, son of Aeacus, but she refused him.

Proteus, an early sea-god, advised Peleus to find the sea nymph when she was asleep and bind her tightly to keep her from escaping by changing forms.

While the Olympian goddesses brought him gifts: from Aphrodite, a bowl with an embossed Eros, from Hera a chlamys while from Athena a flute.

As is recounted in the Argonautica, written by the Hellenistic poet Apollonius of Rhodes, Thetis, in an attempt to make her son Achilles immortal, would burn away his mortality in a fire at night and during the day, she would anoint the child with ambrosia.

When the Trojan War broke out, Thetis was anxious and concealed Achilles, disguised as a girl, at the court of Lycomedes, king of Scyros.

Raising an alarm that they were under attack, Odysseus knew that the young Achilles would instinctively run for his weapons and armour, thereby revealing himself.

However, Achilles feels disrespect for having to hand over Briseis and prays to Thetis, his mother, for restitution of his lost honor.

[12] When she finally speaks to Zeus, Thetis convinces him to do as she bids, and he seals his agreement with her by bowing his head, the strongest oath that he can make.

She vows to return to him with armor forged by Hephaestus, the blacksmith of the gods, and tells him not to arm himself for battle until he sees her coming back.

The Lacedaemonians were at war with the Messenians, who had revolted, and their king Anaxander, having invaded Messenia, took as prisoners certain women, and among them Cleo, priestess of Thetis.

[18] In one fragmentary hymn[19] by the seventh-century BC Spartan poet Alcman, Thetis appears as a demiurge, beginning her creation with poros (πόρος) "path, track" and tekmor (τέκμωρ) "marker, end-post".