The Death of Hercules
Years after the incident with Nessus, Hercules became infatuated with a young woman named Iole. Deianira, learning of her husband's interest in another woman, remembered the "love charm" that Nessus had given her. Believing it would restore her husband's affection, she decided to use it.
Deianira took one of Hercules' tunics and smeared it with the blood Nessus had given her, carefully working the substance into the fabric. She then gave this poisoned garment to a servant named Lichas, instructing him to deliver it to Hercules as a gift from his loving wife. The servant, knowing nothing of the poison, departed on his errand.
The Poison Awakens
The Hydra's venom remained inactive whilst cold, but the warmth of human skin activated its terrible properties. When Hercules put on the tunic and his body heat warmed the fabric, the poison began its work.
The pain was immediate and excruciating. The tunic began to burn into Hercules' flesh, the venom eating through skin and muscle. When he tried to tear the garment off, it clung to him, and strips of his own flesh came away with the fabric. The poison was burning him alive from the outside in.
In his agony and rage, Hercules seized the innocent messenger Lichas and hurled him into the sea with such force that the servant was transformed into a rock before he struck the water. The hero's roars of pain echoed across the mountains as he tried desperately to remove the tunic, succeeding only in spreading the poison further across his body.
The poison spread through all his limbs, eating with invisible decay. He groaned and tried to pull the robe away, but it stuck to his skin; either it clung to his body, or else, when he ripped it, tore away the flesh beneath.
— Ovid, Metamorphoses 9.165-170
When Deianira learned what her "love charm" had actually done, she was overcome with horror at what she had unwittingly inflicted upon her husband. Unable to bear the guilt, she took her own life. Meanwhile, Hercules, realising that the poison would never stop and that he faced an agonising, lingering death, made a fateful decision.
He commanded his followers to build him a funeral pyre on Mount Oeta. When they hesitated, he ordered his son Hyllus to marry Iole (ensuring she would be cared for) and asked his friend Philoctetes to light the pyre. In exchange for this service, Hercules gave Philoctetes his bow and poison arrows - weapons that would later prove crucial to the Greek victory at Troy.
As the flames consumed his mortal body, a miraculous transformation occurred. Zeus, looking down on his suffering son, finally intervened. He sent a thunderbolt to speed Hercules' passage and carried away his divine essence in a cloud. The mortal part of Hercules was burned away in the flames, but his immortal half - the divine spark inherited from Jupiter - ascended to Mount Olympus.
Apotheosis: From Hero to God
On Olympus, Hercules was welcomed amongst the gods. Juno, who had persecuted him throughout his mortal life, finally relented and was reconciled with him. Hercules married Hebe, the goddess of youth, and took his place as an immortal deity. He had achieved what few mortals could: a transformation from man to god through suffering, service, and divine descent.
Zeus made him immortal and brought him to the heavenly halls. He was received by all the gods, even by Juno, who at last put aside her old quarrel. There Hercules enjoys eternal happiness, ageless and deathless, with Hebe for his bride.
— Ovid, Metamorphoses 9.270-273