Celaena is an eighteen-year-old assassin serving a four-year contract as the King's Champion. She lives in the glass castle in Rifthold, balancing her love for fine clothes and books with the heavy burden of her deadly occupation. Despite her fearsome reputation, she secretly spares the targets assigned to her, staging their deaths to protect them while securing her own temporary freedom.

Chaol is the honorable Captain of the Guard in Rifthold. He forfeited his noble title as heir to Anielle to serve the Adarlan crown, completely cutting ties with his demanding family. He constantly struggles to balance his growing romantic feelings for Celaena with his rigid sense of duty to a tyrannical kingdom.

Dorian is the Crown Prince of Adarlan. He previously sponsored Celaena in the fighting tournament and maintains a close, platonic friendship with her after moving past his romantic feelings. He secretly discovers he possesses raw magic, a terrifying realization since his father outlawed and violently eradicated magic across the continent a decade ago.

Nehemia is the Princess of Eyllwe who resides in the glass castle under the guise of an ambassador. She secretly acts as a spy and works to free her people from Adarlan's brutal labor camps. She serves as Celaena's closest confidante and frequently pushes the assassin to take a stand against the empire's cruelty.

The unnamed, tyrannical ruler of the continent. He conquered neighboring kingdoms and outlawed magic a decade ago, enforcing his will through severe punishments and labor camps. He issues regular assassination orders to Celaena to eliminate anyone he suspects of rebelling against his empire.

Archer is a highly sought-after, handsome courtesan working in Rifthold. He trained alongside Celaena at the Assassins' Keep when they were younger. He becomes a primary target for Celaena after the king suspects him of harboring rebel sympathies and orders his execution.

Roland is Dorian's cousin and the king's nephew. He hails from a minor coastal city but earns a sudden, suspicious appointment to the king's council. He frequently inserts himself into Dorian's affairs, wearing a strange black ring identical to the one the king wears.

Elena is the spirit of the first Queen of Adarlan and wife of King Gavin. She appears selectively to Celaena, urging her to uncover the dark mysteries hidden within the glass castle and accept a greater destiny in fighting evil.

Mort is a magical, skull-shaped bronze door knocker guarding Queen Elena's tomb. He retains ancient magic despite the kingdom's ban and provides Celaena with hints about riddles and castle secrets, but only if she asks the correct questions.

Kaltain is a disgraced court lady currently imprisoned below the castle. She suffers from worsening headaches and disjointed memories of being manipulated by Duke Perrington, hearing strange sounds that others cannot perceive.

Baba Yellowlegs is an old witch traveling with a carnival that arrives in Rifthold. She possesses dangerous knowledge about ancient spells, magic, and Wyrdkeys, attracting the attention of characters desperately seeking magical answers.

Fleetfoot is Celaena's loyal dog living in the glass castle. She provides comfort and companionship to the assassin in the quiet moments between assignments and court intrigue.

Perrington is a powerful lord and a close confidant to the King of Adarlan. He is responsible for Kaltain's downfall and continues to work closely with the king on dark political maneuvers, eventually taking Kaltain away to Morath.

Clarisse is a madame operating an elite establishment in Rifthold. She took Archer in from the streets when he was young and currently controls his contracts and financial freedom, acting as his strict employer.

Hollin is the younger brother of Prince Dorian. He is pulled out of school by his mother due to rising rebel threats in the kingdom, and his return sparks a large homecoming celebration at the castle.

The Lord of Anielle is Chaol's estranged father. He arrives at the glass castle upon the king's summons, bringing intense political pressure and old family resentments to his son's doorstep.