Kael is a lean, hard-muscled human man with pale olive skin, sharp gray eyes, and black hair kept short enough to prevent anyone from grabbing it. A thin scar cuts across his left cheek, while older scars mark his wrists and ribs. He wears a weathered leather coat over dark travel clothes, soft boots, and a black scarf that can conceal the lower half of his face. His movements are controlled and nearly silent, giving him the unsettling stillness of a predator waiting to strike.

Kael is quiet, observant, and unnervingly patient. He studies every room before entering it and remembers small details about people that they assumed went unnoticed. His humor is dry and often cruel, especially when someone boasts about wealth or power. He rarely raises his voice, because he believes anger is information that should never be given to an enemy.

Kael Varrin was born into a poor but loving human family in a city where gold could buy almost anything and the lives of the poor were worth almost nothing. His father guarded caravans, his mother repaired clothing, and Kael grew up beside his older brother and younger sister. When Kael was twelve, his father accepted a lucrative caravan job and discovered that the shipment was actually a cargo of kidnapped travelers, prisoners, and desperate families. The merchant responsible sent killers to silence him. Kael hid beneath the floorboards while his home was destroyed, his father was beaten, and his little sister was dragged away. Soon afterward, Kael and the rest of his family were sold through underground markets. His father became a pit fighter, his mother was forced into labor, his brother vanished, and his sister was purchased by an unknown buyer. When his father escaped and tried to rescue them, Kael was forced to watch the merchants murder him as a warning to anyone who resisted. Kael escaped weeks later, but he did not run far. He learned to vanish into crowds, open locks, follow targets, exploit weaknesses, and kill without being seen. His first victim was one of the men who sold his family. After that, he accepted assassination contracts, first against slavers and criminals, then against corrupt merchants and anyone with enough gold to pay. The underworld began calling him the Black Knife. He now travels from city to city as a professional killer while searching for his missing sister. He claims that every murder is justice, but the truth is darker. Revenge became his craft, and killing became the only thing that still makes him feel certain. He will do anything to find his sister, even if completing that search leaves nothing recognizable of the boy he once was.