Egæus is a bookish, sickly intellectual who lives isolated in his wealthy family's ancestral estate. Describing his lineage as a race of visionaries, he suffers from a mental condition he calls "monomania," which compels him to stare at trivial objects for hours in a detached, emotionless trance. He prefers the world of imagination and classical texts over reality, rarely leaving the gloomy library where he was born. As his cousin Berenice's health declines, his typical scholarly fixations shift toward her changing physical appearance.

Berenice is Egæus's cousin, raised alongside him in their grand, decaying family mansion. Unlike her gloomy, studious cousin, she is initially full of life, frequently roaming the natural grounds outside the house. She eventually contracts a form of epilepsy that causes severe physical deterioration and puts her into rigid, deathlike trances. Stripped of her former vitality, she becomes a silent figure in the house, maintaining a quiet presence despite her terrifying symptoms.

Egæus's mother is a deceased member of the visionary aristocratic family. She died in the library of the ancestral mansion while giving birth to her son. Her passing establishes the atmosphere of sorrow and morbidity that pervades the estate and deeply influences her son's psychological development.

The servant is an unnamed staff member working in the gloomy ancestral mansion of Egæus's family. Tasked with managing the practical affairs of the household, the servant acts as a crucial link between the isolated, trance-prone Egæus and the physical realities of the estate.