Archer of Black, whose true name is Chiron, is a central figure in the Great Holy Grail War as the Servant of Fiore Forvedge Yggdmillennia. His origin lies in Greek mythology, where he was known as the great wise centaur, a son of the Titan Cronus and the goddess Philyra. Despite his divine parentage, Chiron lost his immortality after being struck by a hydra-poisoned arrow intended for another, an agony so great he chose to relinquish his eternal life to find peace. This loss of complete divinity ultimately allowed his spirit to be summoned as a Heroic Spirit. Following his death, Zeus honored him by placing his image in the stars as the constellation Sagittarius.

In the context of the Holy Grail War, Chiron is summoned in a human form to obscure his true identity, as his famous centaur shape would be immediately recognizable. He appears as a calm, gentle-looking man with delicate features, clad in archaic leather armor that befits a bowman. His presence is described as being like a vast forest, exuding a cool and clear air. A consistent duty following his summoning was to push Fiore's wheelchair, an act that symbolized their close and trusting partnership.

Chiron's personality is defined by his nobility, deep caring nature, and impeccable courtesy. He is widely respected among the Black Faction for his wisdom, honest character, and sound advice. Lancer of Black entrusts him with command of the front lines, while Rider of Black expresses a desire for him to be their leader, a role Chiron humbly declines, feeling he is unsuited for bearing the full brunt of such responsibility. His primary motivation for seeking the Holy Grail is deeply personal. He wishes for the return of the immortality he gave away, not out of a desire for eternal life itself, but because it was a gift from his parents. He understands that his parents never loved him, yet that immortality serves as the thinnest bond connecting him to them, and he yearns to have that proof of his lineage restored.

Throughout the story, Chiron acts as a pillar of the Black Faction, often serving as a strategist and healer. He is among the first to assess the threat posed by enemy Servants, and his judgment is highly valued. His role becomes crucial when Rider of Black brings him a dying homunculus who escaped from Caster of Black. Using his healing expertise, Chiron examines the homunculus, later named Sieg, and delivers the grim prognosis that he has only a few years to live. He then challenges Rider to take full responsibility for the life he saved, demonstrating his belief in the weight of a hero's decisions.

One of the most significant relationships in Chiron's story is with his former pupil, Rider of Red, whose true name is Achilles. Chiron was Achilles's teacher and mentor for nine years, and their reunion on opposite sides of the war is a source of both great joy and profound sorrow. Chiron knows Achilles's only weakness, his heel, and his deep understanding of his student's character and combat style makes him one of the few capable of countering him. During their encounters, Chiron continues to lecture and instruct his former student, even in the heat of battle, kicking him to safety and reminding him of the limitations of his immortal defenses. Despite their conflict, Chiron is genuinely glad that Achilles has earned his place as a Heroic Spirit, feeling that it would have left a bad taste to slaughter a student one-sidedly.

His relationship with his Master, Fiore, is one of mutual respect and care, resembling that of a teacher and a beloved student. Chiron understands that Fiore works obsessively to overcome the handicap of her immobile legs and that she needs unconditional praise. He comforts her and praises her efforts openly, acting as a source of emotional support and wisdom. In turn, Fiore trusts him completely.

While Chiron does not undergo a dramatic personality shift, his development is seen in his interactions with Sieg. He is strict with the homunculus to balance Rider’s doting nature, believing that because Sieg has such a short lifespan, he cannot afford to be lazy, lest he face only regret at the end. As a transient ghost without a body, Chiron sees value in leaving a mark on the world, even if it is just by helping a single being like Sieg.

As a Servant, Chiron is extraordinarily powerful, considered one of the three greatest weapons of the Black Faction alongside Vlad III and Siegfried. Even when summoned in human form, which lowers some of his parameters compared to his true centaur form, his archery skills remain peerless. He possesses superb physical parameters and a vast reservoir of mana. His combat style relies on his immense experience, cool-headed analysis, and incredible agility to exploit openings that other Servants would not even perceive. His great composure makes it nearly impossible to catch him off-guard through fear or surprise. Despite his lack of a single, overwhelming decisive weapon like some other Servants, his overall strength and wisdom make him a candidate for victory in any Holy Grail War, a cornerstone of his faction's efforts.