Atreus, in Greek mythology, was king of Mycenae, son of Pelope and Hippodamia, grandson of Tantalus, twin brother of Thiestes, and father of Agamemnon and Menelaus.
There are variants on the sons of Atreus:
in Pseudo-Apolodorus, Agamemnon and Menelaus are sons of Plisthenes and Aeope, daughter of Catreu. in Hesiod and Aeschylus, quoted by John Tzetzes, Byzantine poet and grammarian, Plisthenes was the son of Atreus and Erope, and Agamemnon, Menelaus and Anaxibia were Plisthenes' sons with Cleola, daughter of Dias.
The story begins when Atreus and his brother Thiestes murder his half-brother Chrysippus, an extremely handsome boy, illegitimate son of Pelope, instigated by his mother Hippodamia. After the crime, Pelope blames Hippodamia, who kills herself.
The brothers fled to Mycenae, where King Eurystheus took them in.
When Eurystheus marched against the Heraclids, they left the brothers to take over the throne. However, what was to be a temporary position became permanent when the king died in battle. From this moment on, calamities followed in the House of Tantalus.
Atreus wanted to offer his best lamb as a sacrifice to Artemis. While searching his flock, he discovered a golden lamb, which he offered to his wife, Aerope, to hide it from the gods. But she gave the lamb to her lover, Tiestes, the brother of Atreus.
The latter says that whoever has the golden lamb should be king. Atreus accepts, but Tiestes appears with the lamb and claims the throne. But Atreus, on Hermes' advice, challenges Tiestes to give him the throne if the sun goes backwards. Tiestes agrees, Zeus sets the sun going backwards in the sky, and Atreus takes back the throne and drives Tiestes out of Mycenae.
Upon also learning of Aeope's adultery with Tiestes, Atreus devises a plan for revenge, feigns a reconciliation with Tiestes, and invites him to Mycenae. After accepting the invitation, Atreus kills Tiestes' sons and has the meat prepared for his meal.
When Tiestes finishes eating, Atreus orders the children's bones and heads and shows them to Tiestes. Horrified, he curses Atreus and leaves. The curse will continue through Atreus' children and grandchildren.
Tiestes went to Sicyon, where his daughter was a priestess. He was told by an oracle that if he and his own daughter Pelopia had a son, the son would kill Atreus. Tiestes raped his daughter in disguise, but the daughter managed to steal his sword.
Meanwhile Mycenae was ravaged by famine and misery and Atreus consulted an oracle who told him to bring Tiestes back. Atreus searched in Sicyon, but Tiestes was no longer there. However, he developed a passion for Pelopia, who he thought was the daughter of the king of Sicyon.
Since Erope had already been murdered, he asked her to marry him. Ashamed of her rape, Pelopia abandoned the newborn in the mountains, but a shepherd found it and alerted Atreus, who forgave Pelopia for her folly and named the child Aegistus.
Atreus continued the search for Tiestes and sent his sons Agamemnon and Menelaus to look for him. They found him and brought him back to Mycenae, where he was imprisoned. Atreus decided to kill him, and ordered Aegistus to do it. Carrying the sword that Pelopia had kept since the rape, Aegistus prepared for the murder.
However he was overpowered by Tiestes, who recognized the sword and understood that Aegistus was his son. So Tiestes spared Aegistus and ordered him to call Pelopia. When she arrived she learned that the sword was her father's, took it and killed herself.
Then Tiestes told Aegistus to go and tell Atreus that he was already dead. Atreus was pleased and went to make a sacrifice. Tiestes revealed himself and told him that he was the real father of Aegistus, ordering him to kill Atreus. Thus the oracle's prediction was fulfilled.
From that moment on, Tiestes was the king of Mycenae.