Orestes begins the story as an educated young man who feels isolated and alone in the world. When his father was murdered, he was smuggled out of the palace and raised in Athens. He longs to belong to a home rather than drifting through the world. He fantasizes about having grown up in Argos. Gentle and compassionate, Orestes is horrified when he sees the conditions in Argos. He particularly wants to save his sister, Electra, who has been kept in virtual slavery in the palace. He is unsure whether to avenge his father until Zeus demands he leave. Orestes decides he no longer wishes to follow anyone's orders. Orestes describes his own psychological metamorphosis as the end of his youth. From that point on, he is resolved and remorseless, and he feels an overwhelming sense of his own boundless freedom. He does not wish to rule or be ruled, only to unapologetically be his authentic self. His confident knowledge of himself and how he wants to act in the world gives him the strength to defy Zeus. He accepts the consequences of his actions without regretting them and leads the flies and Furies away from Argos.
Zeus is the primary antagonist in The Flies. His character is a personification of power and the moral codes imposed on humans from the outside. Despite his bluster, he uses deception, small tricks, and suggestion to accomplish his ends. He enjoys the piety, remorse, and obedience of the people of Argos, and approves of the way they are cowed into submission. Zeus knows a foretold hero will come to understand his own freedom, and this understanding will signal the end of the gods' dominion on Earth. His powers do not work on someone who knows he is free, so although he threatens Orestes with all the vengeance of heaven, there is nothing he can actually do to compel the young man. In the end, Zeus slinks away, diminished but not yet powerless, saying he pities Orestes for the exile his freedom has brought him.
After Electra's mother killed her father, Electra was kept as the lowest servant in the palace. When Orestes first sees her, she is pouring trash on a statue of Zeus while she declares her hatred for him and for her family. She dreams of the day her brother will come to rescue her and avenge her father. She particularly hates her mother, whom she views as a hypocrite who has never truly loved her. Electra defies Aegistheus by wearing white and dancing happily at the ritual of repentance, where the dead will be released. However, she is embittered when the people of Argos will not be won over by words. Though she is banished, she stubbornly refuses to leave without having vengeance. When Orestes reveals himself to her, she tells him to go because he is too soft for what she needs him for. As Orestes's resolve strengthens, Electra becomes increasingly afraid of him. She urges him to kill Aegistheus but afterward asks him not to kill Clytemnestra. As she stands over Aegistheus's dead body listening to her mother's screams, she wonders if she ever really wanted this at all. Guilt overwhelms her, and she nearly gives herself to the Furies voluntarily. When Zeus offers her absolution in return for servitude, saying her wish for her mother's death was just a child's dream, she accepts his offer.
Clytemnestra is publicly consumed by guilt, and her misery has left her ruined. She makes no effort to change things and seems disinterested in her own life and family. By her own admission, she hated Agamemnon and does not regret his death. Nor does she appear to regret her treatment of Electra, as Electra points out. She says she regrets the loss of her son, but it is difficult to tell if this is merely a lie she does not believe can be disproved. Clytemnestra hates how much of her younger self she sees in Electra. She is certain her daughter's temperament will lead her to ruinous crimes like her own.
Aegistheus was Clytemnestra's lover while Agamemnon was away at war. He helped the queen slay her husband, Agamemnon, upon his return. Aegistheus took over control of the city of Argos and since then has ruled through fear and superstition. Once a year, on the anniversary of the murder, the high priests of Argos roll back a stone and declare that the vengeful dead have come to torment the people, including Aegistheus. Though he knows this is a lie, an exhausted and listless Aegistheus is beginning to believe it himself. Aegistheus questions Zeus about why he was allowed to rule Argos and is unsatisfied with the arbitrary nature of the god's answers. However, he, like Zeus, recognizes that a person aware of their own freedom is a danger to the systems of control they have set in place. When Orestes comes to kill him, Aegistheus does not resist. With his dying breath, he warns Orestes to beware the flies.