Heracles is the legendary son of the god Zeus and the mortal woman Alcmene. He possesses immense physical strength and completes grueling labors for the Mycenaean king Eurystheus to secure his family's return to Argos. Because he is currently away in the Underworld capturing the hound Cerberus, his prolonged absence leaves his household vulnerable to political enemies in Thebes.

Amphitryon is an elderly Argive hero and the mortal foster father of Heracles. He takes pride in his past, specifically that he shared his wife Alcmene with Zeus to produce Heracles. Now weakened by age, he tries to protect his grandchildren from the tyrant Lycus by relying on hope, endurance, and desperate prayers to the gods.

Megara is the daughter of Creon, the deposed king of Thebes, and the wife of Heracles. Trapped by Lycus's violent takeover of the city, she faces the imminent execution of herself and her children. Practical and highly conscious of her noble birth, she prefers an honorable death over futile resistance or false hope.

Lycus is an authoritarian ruler who usurped the throne of Thebes by murdering King Creon. Operating on ruthless political calculation, he plans to execute Heracles's family to prevent the children from seeking revenge when they grow up. He views traditional, solitary heroism with skepticism, arguing that true courage belongs to soldiers in ranks.

Theseus is the famous king of Athens and a steadfast companion to Heracles. Tied to the main hero through a strong bond of mutual assistance, he represents the ideal of loyal friendship. He prioritizes personal bonds over fear of divine pollution or danger.

The Chorus consists of elderly, physically frail men from the city of Thebes. They remain fiercely loyal to Heracles and his family despite their inability to take up arms against Lycus. Their advanced age limits their actions, but they maintain a strong moral stance against the current tyranny.

Iris is the messenger of the gods, acting as a strict enforcer of divine will. She specifically carries out the orders of Hera, who harbors a deep, resentful hatred for Heracles due to his illegitimate birth. She is uncompromising and objective in her punitive duties.

Madness, also known as Lyssa, is a divine personification of frenzy and irrationality. Unlike Iris, she demonstrates an awareness of Heracles's beneficial deeds for both gods and mortals. She shows distinct reluctance to enact the destructive commands forced upon her by higher powers.

The Messenger is a servant attached to the royal household of Thebes. He functions as the traditional bearer of news in Greek tragedy, burdened with the task of describing intense, off-stage events that occur behind closed doors to those waiting outside.