Horace Thomas, eldest biological son of Bert and Joanna Thomas, inherits the family's dark-haired resemblance. Residing in a large, impoverished household, he initially exhibits bratty and antagonistic conduct toward foster child Anne Shirley. He participates in or overlooks the bullying Anne suffers, mirroring the pervasive hostility within the Thomas home.

Deeply impacted by family dysfunction, Horace witnesses his father's alcoholism and violent outbursts. One pivotal incident involves Bert drunkenly destroying Horace's schoolbooks, leaving the boy sobbing as he retrieves the ruined items—a moment revealing suppressed academic frustrations and vulnerability. These experiences cast Horace as both perpetrator and victim within the household's abusive cycle.

Following Bert's death, Horace transforms into a responsible figure. He assists his mother with childcare, household chores, and farm labor, adapting to adversity by assuming a quasi-parental role for his younger siblings. His dynamic with Anne evolves; during crises like Bert's violent episodes, Horace shields her by urgently directing her to hide, demonstrating emerging empathy.

Horace's arc concludes when the Thomas family disbands after Bert's demise. His grandmother relocates him, his mother, and brothers to Bolingbroke, severing ties with Anne.