William is a small, long-limbed farm child with an unusually still way of standing, as if he is waiting for the hillside to finish speaking. His thick black hair grows in stubborn, soft-looking waves that refuse to lie flat, and his bright blue eyes catch lamplight with an almost startling, glassy shine. His cheeks are often wind-roughened; the skin at his nose reddens after a day outdoors. He walks carefully over uneven ground, placing each boot as though he has already noticed the loose stone or hidden rut. Within a minute of meeting him, most people notice him rubbing the frayed edge of a little wool cuff between finger and thumb. The cuff belonged to a lamb he helped save, and its nap has been worn smooth in one narrow strip. He is unexpectedly good at whistling through a blade of grass, though he stops if anyone praises him for it.

William is observant but slow to speak, and his silence can look like either fear or stubbornness. He wants independence, yet takes comfort in the routines and protection of home. With patient people he is unexpectedly dryly funny; under family scrutiny he withdraws and remembers every slight. He is tender toward animals and alert to danger, but resents being treated as though his judgment cannot be trusted.

William Hirst was born after a punishing labor that left his mother, Mary, feverish and exhausted. His father, Oswin, a man accustomed to command, held the newborn with a solemn gentleness the midwife never forgot. William inherited Oswin's startling blue eyes, but his dense black hair resembles neither parent. Mary recovered slowly, and William grew up noticing the small signs of her pain: two fingers at her temple, a measured breath before rising, and the extra effort she made to welcome visitors. Her care was tender, but sometimes she answered for him or kept him from relatives whose scrutiny frightened her. Oswin made time for his son despite the work of the Hirst farm. He taught William to read a flock, notice a lame sheep, judge weather, and find a gap in a hedge. In the fields, William often understood what needed doing before he could explain how he knew. At home, where lessons and questions demanded quick answers, he was slower. Oswin could mistake that pause for hesitation and cut him off; a rare nod of approval mattered more to William than he admits. He resents being handled as fragile, yet longs for both parents' protection. As a child, William once wandered too far onto the moor and found a ewe and her lamb trapped beyond a broken boundary in gathering fog. He led them home by following the wind and the faint sound of the farm bell. The family welcomed him back in relief, then argued over whether the rescue proved anything about his fitness to inherit. That day taught him that being right does not mean people will trust him. His maternal uncles Edmund and Huge, and his maternal grandparents, have made their doubts about the succession increasingly public. Mary challenges them when she can; Oswin watches William closely but seldom explains what he is thinking. William has also heard rumors that two of his mother's pregnancies ended before birth and that a baby son died soon after arriving. One uncle let slip the family's more painful story: a barghest violated Mary by accident on her wedding night. William does not know what to believe about the account, but fears his own birth is being treated as evidence in a family argument. He has noticed that Oswin seems not to age, avoids iron, stiffens in church, and becomes unnervingly formal at certain boundary-crossing seasons and hours. At night, William has glimpsed a tall houndlike shadow near his father. The household calls these odd hours or bad dreams. Locals call William Black William, or Blackby, when Oswin is not close enough to hear. William wants to become capable on his own terms, protect his mother from the family quarrel, and learn what his father is without letting the answer decide what he is.