Atreus was a son of Pelops and Hippodamia and the brother of Thyestes. Their father's story already connected the family with a dangerous bargain. Pelops won Hippodamia after a chariot contest with her father Oenomaus, aided in some versions by the king's charioteer Myrtilus. Accounts differ over the details of the treachery and Pelops's reasons for killing his helper afterwards. Apollodorus describes Myrtilus being thrown into the sea and cursing the house of Pelops as he falls. The curse gives later storytellers a way to connect separate acts of violence across generations, though the family's crimes are not arranged into one identical sequence in every ancient source.

Another early conflict concerns Chrysippus, a favoured son of Pelops by a different mother. In Hyginus, Hippodamia fears that Chrysippus will inherit the kingdom and prompts Atreus and Thyestes to kill him. Hippodamia subsequently takes her own life after Pelops blames her. Other accounts arrange the circumstances differently. What matters to the later rivalry is that Atreus and Thyestes arrive in their struggle for power with an earlier family murder already behind them. Their shared descent does not guarantee solidarity. It gives them a common claim to a throne and a history of treating kinship as something that can be sacrificed for advantage.

The contest for Mycenae turns on a golden lamb. In Apollodorus's account, the Mycenaeans receive an oracle telling them to choose a descendant of Pelops as king. Atreus has vowed to sacrifice the finest of his flock to Artemis, but when the extraordinary lamb appears, he does not fulfil the vow. He kills it and keeps it concealed in a box. His wife Aerope, daughter of the Cretan king Catreus, is in love with Thyestes and gives the precious animal to him. When Thyestes proposes that possession of the golden lamb should determine who rules, Atreus agrees without knowing that the object has already passed into his rival's hands. Thyestes produces it and takes the kingship.

Atreus regains the throne through a second test. Zeus sends Hermes with advice, and Atreus persuades Thyestes to surrender his claim if the sun should travel contrary to its ordinary course. Thyestes accepts what appears to be an impossible condition. Zeus then reverses the sun's movement, establishing Atreus as king. The divine action belongs to Zeus, not to a personal magical power of Atreus. The story also places the heavenly sign at the contest for kingship. In other treatments, the sun turns away in horror at the later banquet. Those are different uses of the motif, not details that must always be combined into two successive astronomical events.

The banquet transforms rivalry into an attack on the bonds of the family itself. After discovering Aerope's adultery and Thyestes's part in the theft, Atreus offers an apparent reconciliation. His brother returns under the protection of that invitation. Atreus has killed children of Thyestes and prepares their flesh as food, concealing what the meal contains until his guest has eaten. He then reveals the remains that identify the victims. The sources vary in the number and names of the children, but agree on the essential deception: a father has unknowingly been made to consume his own offspring. What outwardly resembles hospitality has become the means of destroying a family relationship from within.

The aftermath is developed at length in Hyginus. Thyestes leaves Mycenae, and the story turns towards his daughter Pelopia. An oracle connects his future revenge with a son born from her. In the account of the nocturnal assault at Sicyon, Pelopia does not recognise her attacker, but takes his sword, leaving a means by which his identity can later be discovered. The resulting child is Aegisthus. Atreus subsequently marries Pelopia, misunderstanding her parentage and believing the child to belong to his own household. The revenge he has set in motion thus enters the family he is trying to protect.

Hyginus's account includes the child's exposure and rescue through suckling by a goat before Atreus brings him up. Later, Agamemnon and Menelaus capture Thyestes and bring him to their father. Atreus sends Aegisthus to kill the prisoner, not knowing that he is sending a son against his own biological father. The sword becomes the decisive sign of recognition. Thyestes identifies it, Pelopia is drawn into the discovery of its history, and the concealed relationships of the household are exposed. The story's violence depends repeatedly on people not knowing whose child, spouse or parent stands before them.

Aegisthus turns against Atreus rather than completing the murder he has been ordered to perform. In Hyginus, Atreus believes his rival dead and is making a sacrifice beside the sea when Aegisthus kills him. Thyestes then regains power. Other mythographical accounts are briefer, but the familiar outcome is the same reversal: the child Atreus has raised becomes the means by which his brother is restored. Agamemnon and Menelaus survive and later recover their positions with support from Sparta. Their subsequent stories must also be distinguished. Agamemnon is murdered after his return from Troy; Menelaus is not killed alongside him and has a different homecoming tradition.

The wider House of Atreus carries these earlier crimes into tragedy. Agamemnon's sacrifice of Iphigenia, his killing by Clytemnestra and Aegisthus, and Orestes's revenge place new generations inside conflicts they did not originate. Aeschylus's Oresteia eventually moves the question of retaliation into the trial of Orestes before Athena's court. Atreus himself receives no such reconciliation. His name stands at the head of a house in which an inherited curse and deliberate human choices continually reinforce one another. The Treasury of Atreus at Mycenae belongs to the historical archaeology of Bronze Age burial, while the king's feast and reversed sun belong to the distinct evidence of myth and literature.