|"I would never call loving someone else a weakness. I think living without love at all, any kind of love, is weakness. And the worst kind of darkness."|
|— Kilorn Warren to Mare Barrow, King's Cage|
About ten years before the start of events, Kilorn's father was sent off to war where he died. His remains were sent home in a shoe box. Kilorn's mother ran off after the loss of her husband, leaving Kilorn to fend for himself. He almost starved to death, but kept picking fights with Mare. She decided to share her food with him so she "wouldn't have to kick around a bag of bones."
Kilorn worked as an apprentice for a fisherman named Cully, until his master died. This resulted in Kilorn becoming eligible for conscription. Kilorn enjoys watching Feats of First Fridays because he likes watching Silvers beat each other up. He often bets on the fights with the little money he has.
Kilorn becomes integral to the alliance of Reds and newbloods because he helped dispel some of the mistrust of newbloods among Reds.
After the Nortan Civil War, Kilorn moved to Montfort with many other Nortan refugees. He moves into his own house, a "little place down the hill in the city." He organized charity drives for the Nortan refugees, and petitioned the Montfort government to help war orphans. He becomes increasingly involved in the Montfort government, eventually becoming the Premier of Montfort. As Premier, Kilorn prioritizes education, history, and science. He spearheaded research into Silver and newblood abilities.
Kilorn is very loyal to the Barrow family and the Scarlet Guard. He is jokester and often finds himself in trouble frequently. He teases Mare every chance he can. He sometimes feels jealous about his lack of ability, especially when he works with Mare to rescue newbloods from Maven. Kilorn has a stubborn streak. He becomes defensive when Mare first meets Cal because he feels that their friendship is threatened. Kilorn never lets his lack of an ability keep him from participating actively in the rebellion against the Silvers.
Kilorn has bottle green eyes and tawny (light brown to brownish-orange) hair. He is a foot taller than Mare, and has a long stride. His gait weaves and is off balance because of the years he's spent on his master's fishing boat.
After the Nortan Civil War, Kilorn has grown broader after moving to Montfort. He is filled out by Montfort's healthy food and by being able to live a "less-than-lethal lifestyle."
Kilorn is Mare's only real friend in the Stilts. While they used to beat each other up as children, their friendship has changed as they grew up. They are incredibly loyal to each other. Kilorn consistently shows Mare that he is not afraid of her or her ability. He pledged to be her best friend until the day he dies. Kilorn loved Mare for a long time. He knew she did not feel the same way, but hoped that one day she would. Mare imagines that if she had not met Cal, her life would have included "a friendly marriage to the fish boy with green eyes, children we could love, and a poor stilt home."