In Greek mythology, Aerope was a Cretan princess, daughter of Catreus, who became queen at Mycenae as wife of Atreus (or Pleisthenes) and mother, in most accounts, of Agamemnon and Menelaus. As Atreus' wife she loved Thyestes and gave him the golden lamb that secured the Mycenaean throne—setting the Atreid feud in motion.
Adapted from Wikipedia, "Aerope" · CC BY-SA 4.0
I.From Crete to Mycenae
Aerope was daughter of Catreus son of Minos, sister of Clymene, Apemosyne, and Althaemenes. Apollodorus has Catreus, warned he would die by a child's hand, give Aerope and Clymene to Nauplius to sell abroad; Nauplius spares her and she marries Pleisthenes (elsewhere Atreus). Euripides' lost Cretan Women instead has Catreus find her with a slave and order her drowned—again Nauplius saves her for marriage to Pleisthenes.
Most classical accounts make her mother of Agamemnon and Menelaus by Atreus; others name Pleisthenes as their father, or have Atreus adopt Pleisthenes' sons when the youth dies young. Hyginus also gives her sons Tantalus and Pleisthenes by Thyestes—the children Atreus feeds to his brother in that version.
II.The golden lamb
At Mycenae Aerope becomes Thyestes' lover and steals for him the golden lamb Atreus had hidden—the token by which the Mycenaeans choose their king. Euripides' Electra and Orestes treat her "treacherous Cretan love" as the hinge of the brothers' struggle. Sophoclean and scholiastic notices have Atreus cast her into the sea for the adultery and the theft.
Tragedy made the Atreus–Thyestes–Aerope story famous (Aeschylus alludes; lost plays by Euripides, Sophocles, and others staged it), though no complete drama on the plot survives.