Alastor

Alastor was the name of several characters in Greek mythology;

Epithet of Zeus
Alastor was an epithet of 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, he 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.

Son of Neleus
Alastor was a son of Neleus and Chloris. When Heracles took Pylos, Alastor and his brother, except Nestor, were killed by him. According to Parthenius of Nicaea, he was to be married to Harpalyce, who was taken from him by her father, Clymenus.

Companion of Sarpedon
Alastor was a Lycian and a companion of Sarpedon. He was killed by Odysseus.