Many ancient Greeks evoked avengers in stories to punish those who would harm their families. The concept of mythical avengers originated with Uranus who was a Greek Titan. The Titans were beings that existed before the Greek gods. Uranus was one of the most powerful Titans, but he feared the power of any potential child born to him by the female Titan Gaia. Hence, Uranus would forcibly stop Gaia from bearing his children, which caused her pain. One of those potential children, Cronus, sought revenge against Uranus and castrated him. The violence of this action spawned the creation of three beings: Alecto, Tisiphone and Megara, who became the first avengers. They punished mortals who committed crimes against their families.
The Greeks believed that the soul of a criminal would be punished by avengers for violent crimes like murder, even if no one knew who was the murderer. The Furies are the most common avengers. The gods allowed these entities to punish anyone who committed murder, specifically against a family member. In many ways, the Furies and the avenger myths enforced the customs and laws of ancient Greeks instilling in their people a sense of right and wrong and warning them of punishment for heinous crimes.
The Greek gods were often known from their myths to personalize and influence the daily lives of Greeks. There are many stories where avengers were used as tools for the gods, even if just actions were not required. One story, known as the Slaughter of the Niobids, centered around the Queen of Thebes, who boasted she had more children than the goddess Leto, who is the mother of the Greek gods Apollo and Artemis. As a result, Leto asked Apollo and Artemis to kill the queen's children for that making that claim.
Avengers are often characters who will avenge a disgrace afflicted upon their family. In the Greek story the Telemachy, Trojan War hero Agamemnon was killed by Aigisthos. Aigisthos became the lover of Agamemnon's wife, Clytemnestra, while Agamemnon fought in the Trojan War. Clytemnestra allowed the killing so she could be with Aigisthos. As a result, Agamemnon's son Orestes killed Aigisthos and Clytemnestra. At first, the Furies, known as avengers for many crimes in mythological Greece, attacked Orestes. However, the gods intervened, stating that Orestes was right to avenge to the murder of his father.