During Throne of Glass Kaltain was described as a strikingly beautiful woman with pale skin and narrow waist, enhanced by tight corsets. She had long raven-black hair and sculptured brows above her night dark eyes. Her voice was once rich and cultured.
By the events of Queen of Shadows Kaltain's appearance had changed; she now had a black Wyrd collar around her moon-white throat and no longer wore the extravagant dresses, but a night black dress that was little more than cobwebs and shadows even in the bitter cold. She was small and painfully thin, bordering on gaunt and covered in too many dark bruises to be accidental. She also had a thick scar on her elbow where the Wyrdkey was hidden.
Kaltain was a clever, cunning and extremely ambitious young woman that came to Rifthold with the intention of seducing Prince Dorian and becoming the Queen of Adarlan. She had always believed she was born to be a queen and sought to better her standing in society and said that while she would easily be able to convince Duke Perrington to make her his duchess, duchess wasn’t good enough when Dorian was still unmarried.
There was a fierce side to Kaltain's personality, first demonstrated when she was arrested; she fought the guards and swore she would kill them. When she killed the Valg in the collar she was wearing and uses her shadowfire to burn down a third of Morath in vengeance for what had been done to her, she was a wolf, she was death.
Kaltain had fire magic that was suppressed by the King of Adarlan's spell; she remembers the warmth of the golden flames from when she was a child. Duke Perrington managed to alter the nature of her fire by bonding her with a Valg and implanting a Wyrdkey in her arm. This turned her fire to shadowfire, a black fire that burned without any evidence.
Kaltain was born to the incredibly wealthy Rompier family who, while they are low-born, are rumored to be richer than the King and come from a line of powerful magic users that seemingly disappeared two generations ago. When she was a child, Kaltain possessed fire magic and she remembers the golden fire until it was suppressed by the King's spell.
During the spring before the series began, she happened to meet Duke Perrington and took it as a stroke of luck to manipulate him into inviting her to Rifthold and securing her the position of lady-in-waiting to Queen Georgina.
In Throne of Glass, Kaltain is introduced as a vain and vapid courtier that is relentlessly pursuing Dorian and competes with Aelin for his attention. At the end of the novel, she schemes with Perrington to drug Aelin during her final match with Cain with the intention of making it easier for Cain to kill her.
Perrington claimed that Kaltain drugged Aelin on her own, which leads to Kaltain being thrown into the dungeons as she screams that she will kill Perrington for what he did to her. As Perrington and the King discussed Kaltain, Perrington confessed that he had been using his power to subtly manipulate Kaltain but the power was taking its toll on the woman, leaving her drained and complaining of headaches; something that Kaltain blamed on her opium addiction.
Kaltain was still in the dungeon during the events of Crown of Midnight with nothing more but a bucket and a pallet of hay. She was half-mad from her opium withdrawals and her long confinement, constantly complaining of flapping wings and headaches. The guards were known to turn a blind eye when Duke Perrington visits her. She began to suspect what Duke Perrington wanted her for; not for her to be his wife but for something else. Kaltain told Aelin that something was coming and she was to greet it. Not long after she was taken away by Perrington under the pretense that he was going to marry her.
During the sequences in Morath, Kaltain was seen to be enslaved to Duke Perrington, who had bonded her with a Valg demon. Manon noted that she appeared lifeless, displaying no outward emotions or reactions to her surroundings, calling her a shell and a weapon. Manon even contemplated attacking Perrington just to see Kaltain's reaction.
Kaltain eventually managed to kill the Valg inside her by lulling it into a false sense of security and pouncing on it, burning it away with her shadowfire. Manon and Elide came across her during their escape, and she extracted the Wyrdkey from her arm, telling Elide to give it to "Celaena Sardothien" as thanks for a warm cloak in a cold cell. She subsequently destroyed much of Morath using her shadowfire, not wanting to live with what has been done to her. She burned herself to ashes in the process.'