Ion is a young man who serves as the caretaker of Apollo's sanctuary in Delphi. Having never known his parents, he considers the temple his true home and lives a tranquil, devoted life. He is introduced happily maintaining the temple floors, grateful for what he calls his life of 'happy slavery' in service to the gods. Despite his contentment, he harbors a deep, lingering desire to discover the identity of his birth mother, and he remains highly wary of the political complexities and xenophobia of the outside world.

Creusa is an Athenian noblewoman and the daughter of the legendary King Erechtheus. She is married to the foreign war hero Xuthus, and their union has remained childless for years, prompting their desperate journey to the Delphic oracle. Beneath her regal exterior, she carries profound emotional pain and harbors a closely guarded resentment against the god Apollo regarding a past trauma. She thinly veils her own painful history by claiming to seek the oracle's advice on behalf of a friend who was wronged by a god.

Xuthus is a renowned war hero from Thessaly who earned his marriage to Creusa through gallantry in battle on behalf of Athens. Desperate for an heir, he is highly credulous when consulting the oracles. He initially receives a prophecy at the shrine of Trophonius before arriving at Delphi, demonstrating his deep reliance on religious omens to secure his family's future. He is a pragmatic, traditional Greek man focused on securing his legacy, though his foreign birth makes his position in Athenian society tenuous.

Hermes is the messenger god and the son of Zeus and Maia. He serves as the bridge between the audience and the mythic events, providing the necessary exposition about the characters' hidden histories and the divine forces at play. He establishes the time, place, and divine stakes of the tragedy before fading from the immediate action.

The Chorus consists of Creusa's loyal handmaidens who have accompanied her from Athens. They marvel at the sanctuary's architecture, observing depictions of Hercules and the Gigantomachy, before turning their attention to the human drama unfolding before them. They act as a sounding board for Creusa's emotional anguish and fiercely advocate for women wronged by powerful men or gods.

An elderly and nearly blind servant of the Athenian royal household. He requires physical support to navigate the sanctuary steps but possesses a sharp, unforgiving mind when it comes to defending Athenian hegemony. His advanced age does not diminish his willingness to take drastic, even violent, action to protect his mistress and her royal standing.

The Pythian priestess is the famous oracle of Apollo at Delphi. She represents the institutional power of the Delphic sanctuary and interprets the god's will for pilgrims. Her quiet adherence to Apollo's long-term instructions guides the mortals toward their ultimate destiny, and she serves as a surrogate maternal figure for the orphaned caretaker of the sanctuary.

Though he does not appear on stage, the sun god Apollo is a central force in the narrative. He is the master of the Delphic sanctuary and the source of the prophecies that drive the characters' actions. He is revered by his temple servants but secretly despised by Creusa for his past mistreatment of her.