The Shirt of Nessus was the poisoned shirt that led to the death of the Greek demigod Heracles. When Heracles and his wife Deianeira tried to cross a river, the centaur Nessus offered to help. However, when Heracles was on the opposite riverbank, Nessus tried to rape Deianeira. The demigod shot an arrow that had been dipped in the poisonous blood of the Lernaean Hydra, and killed Nessus. Just before he died, though, Nessus told Deianeira to take his shirt, which was covered in the now tainted blood of the centaur; she was told to use his blood to make sure that her husband would forever be faithful to her. Deianeira naively believed the centaur and took his blood-covered shirt.
Years later, when Heracles fell in love with Ino, Deianeira felt jealous and threatened; so, she gave Heracles the shirt of Nessus. As soon as the hero wore it, he started feeling unbearable pain, as his body started burning. He eventually threw himself into a funeral pyre, and died.