There are two characters named Deianira in Greek mythology. The name means "the destroyer of her husband". The lesser known character is an Amazon that was killed by Heracles while performing one of his Twelve Labours, which was to acquire the girdle of Hippolyta, queen of the Amazons.
The best known Deianira was the second wife of Heracles. She was the daughter of Oeneus, king of Calydon, and Althaea, and she had one brother, Meleager. In one account, it is mentioned that her beauty was such that she was wanted by both Heracles and the river god Achelous. Her father had already given her to Achelous, but Deianira did not like him, as he was able to take the form of a serpent, a man with the head of a bull or a bull. Heracles managed to defeat the god and claim Deianira as his wife.
Deianira, however, also became the cause of her husband's death. Nessus, a centaur, tried to rape Deianira, but Heracles shot him down with a poisoned arrow. As he lay dying, Nessus told Deianira to take some of his blood, mix it with olive oil and thus make a potion that would keep her husband faithful to her. She believed him and kept the potion a secret. Heracles, adventuring all over Greece, fathered various illegitimate children and eventually fell in love with Iole. In fear of being abandoned, Deianira smeared the potion on Heracles' shirt (which since then was called the Shirt of Nessus). When Lichas, Heracles' servant, gave the shirt to the demigod, Heracles wore it and immediately started getting burned by Nessus' toxic blood. To stop the pain, Heracles ultimately threw himself into a pyre and died. Deianira, realising what happened, killed herself by hanging herself.