Stephen is a strong, athletic girl who prefers riding horses and roughhousing over traditional feminine pursuits. Growing up at Morton Hall, she manages her mother's disapproval alongside a growing awareness of her attraction to women. She finds comfort in her father's quiet acceptance and her burgeoning writing career.

Lady Anna is an aristocratic Irishwoman who prizes traditional femininity. She struggles to understand her daughter's masculine traits, creating emotional distance within the household. Her rigid adherence to societal norms ultimately dictates how she treats those closest to her.

Sir Philip is a compassionate, outdoorsy nobleman who adores his daughter and encourages her physical development. He quietly recognizes Stephen's differences but chooses to support her silently rather than force her into a traditional mold. His study serves as a safe haven for Stephen.

Miss Puddleton, affectionately known as Puddle, is a strict educator who recognizes and cultivates Stephen's literary talent. She acts as a fierce protector and surrogate mother to Stephen. She understands her pupil's struggles with societal expectations better than anyone else in the household.

Mary is a young Welsh orphan who escapes a restrictive life working for relatives to join the war effort in France. She proves surprisingly resilient on the front lines as an ambulance driver. She quickly forms a deep bond with Stephen while seeking affection and stability.

Angela is an American former actress who married into wealth to escape poverty. She projects a fragile pale beauty but uses her charm to manipulate those around her. She seeks excitement to distract from her unhappy marriage.

Martin is an outdoorsman from British Columbia who loves trees and horseback riding. He quickly becomes a comfortable companion for Stephen because he accepts her without judgment. His relationships become complicated by his growing romantic feelings.

Jonathan is an eccentric playwright who recognizes Stephen's literary talent and pushes her to experience life more fully. He serves as an unpredictable guide, introducing Stephen to artistic circles in Paris.

Valérie is a respected artist and salon hostess in Paris who openly lives as a lesbian. She maintains a calm demeanor while providing a safe gathering place for individuals ostracized by mainstream society.

Mademoiselle Duphot is a lonely French governess who attempts to teach Stephen her native language. Though somewhat disorganized, she genuinely cares for her young charge and shares stories of her family's misfortunes in France.

Roger is a boastful neighbor boy who enjoys teasing Stephen about her lack of femininity. He carries this arrogant attitude into young adulthood, often causing distress for Stephen through his social maneuvering.

Violet is Stephen's fragile neighbor who fully embraces traditional feminine expectations. She frequently offers unsolicited advice on how Stephen should dress and behave, treating social milestones as opportunities to gloat.

Ralph is a retired magnate who uses his wealth to control his wife, Angela. He is easily angered, frequently insults Stephen, and holds his financial rescue over Angela's head to maintain dominance.

Jaime is a large, proud musician living in a cramped Paris apartment. She struggles with poverty and the stress of caring for her frequently ill partner, finding moments of joy only when surrounded by understanding friends.

Barbara is Jaime's longtime companion. She suffers from poor health and the strains of poverty but maintains a cheerful demeanor when spending time with trusted friends.

Collins is a timid housemaid at Morton Hall who occasionally humors young Stephen's roleplaying games. She suffers from an injured knee and eventually seeks romance with one of the footmen.

Williams is the hardworking stud groom at the Gordon estate who shares Stephen's deep love for horses. He takes immense pride in his work and views the animals in his care with almost religious reverence.

Raftery is Stephen's prized Irish horse and most trusted confidant. He represents freedom and loyalty, offering Stephen a silent, understanding presence during her most isolated moments at Morton Hall.

Julie is Mademoiselle Duphot's blind sister who supports herself by making intricate lace. She welcomes Stephen into her home and appreciates the kindness and generosity shown to her family.

Mrs. Bingham is the strict housekeeper at Morton Hall who enforces discipline and traditional boundaries. She frequently clashes with the unruly young Stephen over matters of hygiene and prayers.

Mrs. Breakspeare is the pragmatic commander of a frontline ambulance unit during World War I. She values efficiency and safety, stepping in to manage the emotional dynamics of her unit when they threaten operational effectiveness.