André Grandier, often referred to simply as André, is introduced as a young boy serving the aristocratic Jarjayes household. His background is one of humble origins, having lost his father at an early age and being raised by his mother until her death, after which he came to live with his grandmother. This grandmother serves as the nanny for the Jarjayes family, which is how André becomes a constant presence in the life of Oscar François de Jarjayes, the general's youngest daughter who is being raised as a son to inherit the family's military legacy.

As a child, André and Oscar are inseparable companions. They are raised together, learning the arts of fencing and horsemanship side by side, which forges an unusually close bond that transcends the typical master-servant dynamic of 18th-century France. Despite being a commoner and the grandson of a servant, the young André is brought up within the Jarjayes estate without a strict regard for the class distinctions that govern society. Consequently, he speaks to Oscar with a casual familiarity that often surprises others and draws reproaches from his grandmother, who worries he is receiving special treatment far above his station.

Personality-wise, the young André grows into a passionate and deeply sensitive individual. He is defined by a strong sense of justice and an innate empathy for the struggles of the common people, a perspective that sets him apart in the opulent and increasingly detached world of the aristocracy at Versailles. Even from a young age, he is observant of the rigid social barriers that separate him from Oscar. This awareness fosters a quiet, internal torment, as he harbors a secret and forbidden love for her—a love he considers impossible due to the vast chasm between his status as a third-estate commoner and her noble birth.

His primary motivation is the protection and companionship of Oscar. While she is initially drawn to the glamorous world of the court and the Swedish Count Fersen, André remains a steadfast, if often anguished, presence at her side. He serves as her footman and confidant, acting as a constant reminder of the world outside the palace walls. His role in the story is that of the loyal childhood friend whose unspoken devotion provides a sharp contrast to the political intrigues and romantic disappointments Oscar experiences in her public life. He is her moral anchor, often voicing support for the commoners and questioning the injustices of the aristocratic system that elevates Oscar while keeping him in the shadows.

Key relationships define his development. His relationship with Oscar is the central axis of his existence, evolving from childhood playmates to a complex dynamic of master and servant, and finally to mutual romantic recognition. He also shares a tense rivalry with Alain de Soisson, a nobleman forced into poverty, who resents André for his privileged upbringing within the great Jarjayes household despite his common birth.

André's notable abilities are rooted in his upbringing alongside Oscar. He is a highly skilled swordsman and an excellent horseman, having received the same rigorous training as his mistress. These skills prove essential as the story progresses into the more volatile period of the French Revolution. However, his physical prowess is tragically curtailed when he loses his left eye. This injury occurs during a battle with a figure known as the Black Knight, when a whip strike damages his eye. Defying his doctor's orders to rest, he rushes to rescue Oscar, a choice that leads to the complete loss of that eye. The strain on his remaining eye gradually blurs his vision, and he eventually becomes completely blind, a condition he tries desperately to hide to continue serving as Oscar's protector.