Achilles was the Hero of the Iliad and was a key fighter in the Trojan War. He was a invulnerable except for his heel, as his mother Thetis had held him by the heel as she dipped him in the river Styx . Despite these efforts, Thetis knew that in the Trojan war he would die, and she accordingly appears in the epic either grieving with her son or pleading to Zeus to help the Argives with whom he fought.
Although Achilles was on the side of the Argives, the altercation between he and Agamemnon in the beginning of the book resulted in he and his forces, the Myrmidons, staying at the ships and letting the Trojans beat the Greeks all the way back to their ships. Eventually, though, his greatest friend Patroclus pleaded to fight the Trojans, who threatened to burn the Argive fleet. Achilles let him go, in his armor, and thus the Greeks fought back with great fervor, thinking that invulnerable Achilles had joined the fight. When Patroclus was slain in battle, the Trojans rejoiced, and Achilles wept. From then, he fought with ferocious intensity, eventually killing Hector. After the Iliad ends, he is killed by Paris with an arrow to the ankle.