Thetis is a sea-nymph, a spirit of the sea, and the mother of Achilles. Her devotion to him is one of her defining characteristics; according to Greek myth, Thetis was so protective over her son that she dipped him in the River Styx when he was a baby in an attempt to make him immortal. Her singular preoccupation with preserving her son’s life in the face of a prophecy that he will die young is reflected in Book 18, when she delivers a lengthy lament to her fellow sea-nymphs in which she preemptively mourns him. Just prior, Achilles decided to avenge Patroclus’s death even though he knows he is fated to die on the battlefield. Unable to prevent her son’s fate, Thetis commits a final, desperate act of maternal devotion and commissions Hephaestus to make Achilles a spectacular new set of armor. Homer’s detailed description of Achilles’ new armor is one of the most famous passages in The Iliad and has inspired many artistic renditions over the years. 

Thetis also highlights the vindictive, flippant ways in which gods interfere with mortals. At the start of the epic, Achilles refuses to fight because he has been insulted by Agamemnon. Achilles complains to his mother, who convinces Zeus to aid the Trojans so that she can punish the Greek army on her son’s behalf. Her meddling in Achilles’s childish feud directly causes the deaths of many innocent soldiers, some on her son’s own side. Thetis’s interference during demonstrates that gods often play with mortals for their own often petty means, with disastrous, large-scale consequences for the mortals in question.