Martin is a psychiatrist working at a mental hospital in 1970s Britain. Despite his success in treating troubled children, he feels profoundly disillusioned with his profession and his passionless marriage to Margaret. He harbors a deep fascination with ancient Greek rituals and secretly envies the intense, albeit destructive, passion experienced by his patients. He increasingly views his job of "normalizing" children as a form of spiritual execution.

Alan is a 17-year-old boy committed to Martin Dysart's psychiatric care after violently blinding six horses with a hoof-pick. He works at an appliance store during the week and grooms horses at a local stable on weekends. Raised in a home fractured by opposing ideological forces, Alan is socially alienated and extremely guarded. He channels his repressed desires into a highly secretive, self-invented mythology centering around horses.

Dora is Alan’s devoutly Christian mother. She filled Alan's childhood with biblical tales of divine judgment and stories about horses, hoping to provide him with moral structure. She is highly protective of her son and deeply defensive about her parenting, harboring a strong skepticism toward psychiatry and the suggestion that she might be responsible for Alan's violent outburst.

Frank is Alan’s father, a staunch atheist and socialist who works at a printing press. He is rigid in his rationalism, openly despising religion and television. He frequently clashes with his wife over how to raise their son, attempting to impose intellectual control over the household. Despite his strict outward morality, he struggles with his own hidden desires.

Jill is a confident young woman who works at Harry Dalton's stables. Friendly and lightly provocative, she shares Alan’s affection for horses but views them simply as beautiful animals to care for. Her earthy, practical familiarity with the horses contrasts sharply with Alan's intense spiritual obsession.

Hesther is a court magistrate who strongly believes in institutional rehabilitation. Horrified by Alan's crime but recognizing his deep psychological pain, she advocates for him to receive hospital treatment rather than a prison sentence. She acts as a sounding board for Dysart, though she maintains a much more conventional faith in the value of a normal life.

Harry is the pragmatic owner of the stables where Alan and Jill work. He views Alan's crime with absolute disgust, representing a punitive view of justice. He believes the teenager belongs in a prison cell rather than taking up resources in a psychiatric hospital.

Margaret is Martin Dysart’s wife. According to Martin, she spends her time knitting clothes for orphans and maintains a puritanical outlook on life. Their marriage is defined by routine rather than intimacy, representing the sterile existence Martin wishes to escape.

Equus is the fictional, all-seeing horse-deity invented by Alan Strang. Forged from a blend of Christian liturgy, advertising slogans, and equestrian imagery, Equus serves as the divine focus of Alan's intense worship. The entity demands absolute obedience and becomes a vessel for the boy's spiritual and sexual longings.

Nugget is a specific horse kept at Harry Dalton's stables. Under Alan's care, Nugget transitions from a regular stable animal into the primary physical avatar of the horse-god Equus. Alan grooms him with meticulous attention during the day and subjects him to secret riding rituals at night.

A staff member working at the psychiatric hospital. She assists Dr. Dysart with administrative tasks and patient care, taking responsibility for moving Alan to and from his designated room.

An athletic young man who rides his horse along the shoreline. He lifts a young Alan onto his horse's shoulders for a thrilling ride, inadvertently sparking the boy's lifelong fixation before clashing with Alan's parents over the unauthorized interaction.