ÆGISTHUS, in Ancient History, was the son of Theites by his own daughter Pilopeia; who, to conceal her shame, exposed him in the woods; some say he was taken up by a shepherd, and suckled by a goat, whence he was called Ægisthus. He seduced Clytemnestra the wife of Agamemnon and lived with her during the siege of Troy. Afterwards with her assistance he slew her husband, and reigned seven years in Mycenæ. He was, together with Clytemnestra, slain by Orestes. Pompey used to call Julius Cæsar Ægisthus, on account of his having seduced his wife Mutia, whom he afterwards put away, though he had three children by her.