Thyestes is the exiled brother of the king of Argos, returning to the city under the promise of a reconciliation. He previously seduced Atreus's wife and stole a magical golden-fleeced ram, igniting a bitter feud for the throne. He vacillates between a philosophical appreciation for his quiet exile and a lingering ambition for his lost power.

Atreus is the cruel king of Argos, consumed by a desire to avenge past wrongs committed by his brother. He views absolute power as the right to act without restraint, rejecting conventional morality and the advice of his attendants. He harbors ongoing doubts about his wife's fidelity and the true paternity of his heirs.

The Chorus is a collective group representing the citizens of Argos. They observe the unfolding events and reflect on the nature of true authority, advocating for self-control and philosophical seclusion over tyranny. They hold a traditional, Stoic worldview but occasionally fail to recognize the depths of human wickedness taking place in the palace.

Tantalus is the sinful patriarch of the royal house of Argos. He is dragged from his eternal punishment in the underworld to infect his descendants with his own erratic, destructive passions. His presence establishes the hereditary curse afflicting his family.

The Fury is a divine agent of the underworld who orchestrates the supernatural prologue. She forces Tantalus to travel to Argos to spread chaos and evil among the royal house, representing the unseen forces driving the family's violent fate.

The Servant is an attendant to the king of Argos who tries to act as a voice of reason. He urges his master to adhere to proper moral conduct, though his cautious counsel is swiftly rejected by the tyrannical ruler.

Tantalus Junior is the son of Thyestes, named after his infamous great-grandfather. He encourages his father to put aside his fears and trust the king's offer of reconciliation, unaware of the trap laid for them.

Agamemnon is one of Atreus's presumed sons. He is sent alongside his brother to deliver the message of a sham reconciliation, deliberately kept in the dark about the true nature of the royal plot.

Menelaus is another of Atreus's presumed sons. Like his brother Agamemnon, he acts as an unwitting participant in his father's scheme to lure their exiled uncle back to the city.

The Messenger is an attendant within the royal house. He observes the secret actions of the king and emerges to recount the grim proceedings to the citizens outside.