Celaena is an 18-year-old orphaned assassin who has spent the last year performing grueling labor in a death camp. When offered a chance to win her freedom by competing to become the King's Champion, she travels to the glass castle in Rifthold under the alias Lillian Gordaina. Despite her deadly skills and traumatic past, she retains compassion for the oppressed, a love for fine clothes, and a fierce intelligence.

The 19-year-old Crown Prince of Adarlan possesses a bookish intelligence that contrasts with his public reputation as a careless flirt. He sponsors Celaena in the King's tournament primarily to annoy his tyrannical father, but he soon develops genuine feelings for her. He feels alienated from his family's cruel imperial legacy and looks for ways to exert his own agency against his father's wishes.

At 22 years old, Chaol serves as the Captain of the Adarlan Guard. He surrendered his noble title as the Lord of Anielle to work at the glass castle, placing duty and law above personal ambition. Rigid in his moral code, he initially views Celaena as a dangerous criminal but gradually forms a connection with her as they train together.

The Princess of Eyllwe is a strong-willed young woman whose home kingdom actively resists Adarlan's occupation. She pretends to speak only her native language to eavesdrop on the Adarlan court. Bonding with Celaena over shared ideals and a hatred of slavery, she quietly searches for ways to support her people from within enemy territory.

The nameless ruler of Adarlan is a brutal conqueror who enforces absolute obedience from his family and his court. A decade earlier, he outlawed magic and ordered the mass execution of magical beings across the continent. He organizes the secret competition to find a personal assassin capable of eliminating his political rivals.

A high-ranking nobleman who acts as the King's enforcer and political lackey. He wears a mysterious black ring matching the King's and takes a disturbing interest in the younger ladies of the court. He sponsors his own ruthless competitor in the tournament while quietly manipulating court politics to serve the empire's expansionist goals.

A wealthy, ambitious noblewoman residing at the glass castle. She relies on opium to manage severe headaches while actively plotting her social ascent. Desperate to secure her future by marrying Crown Prince Dorian, she views his mysterious new female companion as a direct threat to her plans.

A massive soldier from the White Fang Mountains chosen by Duke Perrington to compete in the King's tournament. Known for his sheer physical dominance, he quickly emerges as the most dangerous competitor in Rifthold. He goes out of his way to intimidate the other participants and holds a specific grudge against Celaena.

A quick-handed thief from Terrasen participating in the King's tournament. He relies on his agility and street smarts rather than brute force. He forms a quiet alliance with Celaena after she offers him advice on improving his knife-throwing technique.

The long-deceased first Princess of Terrasen and first Queen of Adarlan. As a spirit, she reaches across the boundaries of death to offer cryptic warnings about a dark force gathering within the glass castle, urging Celaena to intervene.

The King of Assassins who took Celaena in when she was an orphaned child. He forced her into a brutal training regimen, ensuring she became the continent's most lethal killer while binding her to his service through financial debt.

A loyal lady-in-waiting who helps maintain Celaena's cover story as a jewel thief named Lillian. She enjoys dressing Celaena in fine gowns and encouraging her to participate in courtly life, providing a touch of domestic normalcy.

The Queen of Adarlan and Dorian's mother. She focuses heavily on court gossip, matchmaking, and ensuring her eldest son produces a royal heir, remaining willfully detached from the kingdom's darker realities and atrocities.

A fellow assassin who was murdered shortly before Celaena was betrayed and sent to Endovier. His memory deeply influences her hesitance to open her heart to anyone new, leaving her with lasting trauma.

The royal Weapons Master who designs the tests for the King's tournament. He maintains strict discipline among the cutthroats and criminals competing for the title, closely watching their progress.

A small, silver-gold puppy saved from being culled. She becomes a comforting companion for Celaena in the isolated environment of the royal apartments, bringing a rare touch of joy to the assassin's daily life.

The younger brother of Crown Prince Dorian. He is a spoiled and violent child who is currently away at boarding school, taking after his tyrannical father much more than his older brother does.