Alastor (Ἀλάστωρ, English translation: "avenger") refers to a number of people and concepts in Greek mythology:
Alastor was an epithet of the Greek god Zeus, according to Hesychius of Alexandria and the Etymologicum Magnum, which described him as the avenger of evil deeds, specifically, familial bloodshed. As the personification of a curse, it was also a sidekick of the Erinyes. The name is also used, especially by the tragic writers, to designate any deity or demon who avenges wrongs committed by men. In Euripides' play Elecktra, Orestes questions an oracle who calls upon him to kill his mother, and wonders if the oracle was not from Apollo, but some malicious alastor. There was an altar to Zeus Alastor just outside the city walls of Thasos.By the time of the 4th century BC, alastor in Greek had degraded to a generic type of insult, with the approximate meaning of "scoundrel".,
Alastor, a son of Neleus and Chloris. When Heracles took Pylos, Alastor and his brothers, except Nestor, were killed by him. According to Parthenius of Nicaea, he was to be married to Harpalyce, who, however, was taken from him by her father Clymenus.,
Alastor, a Lycian, who was a companion of Sarpedon, and was slain by Odysseus.Alastorides is a patronymic form given by Homer to Tros, who was probably a son of the Lycian Alastor mentioned above.,
Another, unrelated Alastor is mentioned in the Iliad of Homer.,
Alastor, in Christian demonology, came to be considered a kind of possessing entity. He was likened to Nemesis. The name Alastor was also used as a generic term for a class of evil spirits.