Olivier, formally titled Olivier of Obsidian, serves as a Paladin in the Chasseurs, a Catholic Church-affiliated holy knight order dedicated to vampire hunting. Ranked as Paladin of the Third Unit, he earned the nickname "Olivier of the Obsidian" through the distinctive black obsidian stone bestowed upon him. Physically, he presents as a slim, pale-skinned man of average height. His long, dark hair, noted for its smoothness and shine, typically cascades down in a loose ponytail reaching his hips, often falling over the left side of his face to cover one eye. He possesses a thin, angular face featuring narrow, upturned eyes framed by long eyelashes and defined eyebrows – characteristics he self-awarely acknowledges as handsome. His attire is the standard Chasseur uniform: black pants, a cassock, a white harness, a purple ribbon-like belt, and dark leather boots. A dark purple rosary symbolizing obsidian adorns his neck (appearing white in the anime adaptation), and his hands are protected by dark, scaled armored gloves.

Olivier exhibits a high-strung and easily agitated personality, particularly provoked by the impropriety of his close friend Roland Fortis. He values efficiency and strict adherence to protocol, displaying impatience towards those who deviate from procedures or act unreasonably. Despite this, he maintains polite and reserved manners with acquaintances. An undercurrent of narcissism and pride exists; he acknowledges his popularity with both men and women yet remains detached from romantic entanglements, believing his father will ultimately arrange his marriage. He smokes cigarettes and occasionally displays laziness, preferring others to handle decision-making. Beneath his irritable exterior lies deep loyalty, perceptiveness, and a capacity to account for others' emotions, especially concerning Roland. He demonstrates fierce protectiveness toward those he trusts, willing to physically confront colleagues like Gano over callous remarks about Astolfo Granatum's family tragedy.

His background includes a decade-long friendship with Roland Fortis. Olivier originally recommended Roland for the position of Emerald Paladin, hoping to instill responsibility, though Roland's persistent flippancy continues to frustrate him. Roland previously served as Olivier's vice-captain before leading his own unit. Olivier also knew Astolfo Granatum from their youth, understanding the complexities of Astolfo's family situation and viewing him with a mix of protectiveness and exasperation.

His duties and relationship with Roland drive his involvement across story arcs. He first appears investigating seismic disturbances caused by Roland's actions during the Hunters of the Dark Arc, where Roland assists Vanitas and Noé's escape. Upon learning of Roland's newfound belief in human-vampire coexistence, inspired by witnessing Vanitas and Noé's friendship, Olivier reacts with concern, warning Roland to hide these views from other Chasseurs to protect him and his family from reprisal. Later, during the Return of the Beast Arc in Gévaudan, Olivier locates Roland researching vampiric history in Mira's laboratory and reiterates his warning about the dangers of his shifting beliefs. When Roland jokingly contemplates fighting fellow Paladins, Olivier interprets it as a veiled threat. In Gévaudan, Olivier coordinates with Roland to combat the Beast while expressing frustration over Roland's tendency to attract trouble. Their partnership continues during the confrontation with the merged wolf beast, where they fight in sync despite Olivier's visible irritation. A subsequent encounter occurs in a Paris café where Olivier and Roland converse with Vanitas. Olivier observes Vanitas's distress, indirectly apologizes for Roland's behavior, participates in a discussion about romantic feelings, and deduces Vanitas's connection to the Blue Moon clan. He later cautions Roland about potential Church efforts to capture Vanitas.

Olivier wields Hauteclaire, a unique blade resembling a non-rotating chainsaw designated "Noble Black." His combat style is notably brutal and reckless, frequently damaging or breaking the weapon during engagements, yet his skill and strength earn respect among the Paladins.

His relationship with Roland remains central. Olivier functions as Roland's anchor, compelling him to articulate his intentions and acting as a voice of caution against his idealism. He openly states that Roland's faith resides not in God but in himself as God's follower. Their dynamic blends deep mutual trust with constant bickering, exemplified when Roland steals Olivier's cigarette, prompting Olivier's annoyed demands for its return. Roland's near-fatal injury protecting Olivier reveals the depth of their bond; Olivier remains at his bedside and privately resolves to leave the Church if Roland does not recover. Olivier also exhibits a protective, almost fraternal dynamic toward Astolfo Granatum, whom he has known since childhood. He intervenes when Gano mocks Astolfo's family tragedy, nearly escalating to violence. Conversely, Olivier harbors active dislike and distrust toward Gano, refusing even basic greetings due to Gano's troublemaking tendencies and lack of empathy.

The character draws inspiration from Oliver, Roland's close friend and confidant in the medieval French epic *The Song of Roland*, part of the Matter of France legends. Within this context, Olivier shares his literary counterpart's role as a voice of wisdom and reason alongside the more reckless Roland, and their story culminates in them dying together at the Battle of Roncevaux Pass. Olivier shares a character song titled "Na mo Naki Michi" with Roland, performed by their Japanese voice actors. He is 27 years old, with a birthday on November 3. His exact height and weight remain unspecified.