ÆGISTHUS, in ancient history, was the son of Thyestes by his own daughter Pilepeia, 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 Ægithus. 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 Mycene. He was, together with Clytemnestra, slain by Orestes. Pompey used to call Julius Cæsar Ægithus, on account of his having seduced his wife Mutia, whom he afterwards put away, though he had three children by her.