Aka no Rider

赤のライダー

Is the Rider-class Servant of Shirou Kotomine of the Red Faction in the Great Holy Grail War of Fate/Apocrypha.

Spoiler

Rider's true name is Achilles (アキレウス), one of the famous heroes in the Trojan Wars. Born from the sea goddess Thetis and the hero Peleus, Achilles was blessed by the gods from birth. His mother Thetis, having greatly loved her son, had warmed him within holy flames in order to try and make him immortal. But her husband Peleus had opposed it, saying "Then that would destroy Achilles as a human," and in the end Achilles grew up while only a certain part of him remained human.
When Achilles was a young child, his mother Thetis returned to her home at the bottom of the sea, due to discord with his father Peleus. Chiron, who had raised many heroes, was an old friend of Peleus. Peleus requested Chiron to train his son and Chiron happily accepted the role of mentoring Achilles for nine years.
After having grown up, he participated in the Trojan War as part of the Achaean army and continued achieving many great feats. He was a human who was exceedingly close to the level of the gods. A fast-sprinting hero with an invincible body, his body blessed by all the gods could never received any wounds, but his heel alone was this hero's vital weak point. The spear his father had given to him pierced through all other heroes. With his chariot led by three steeds, consisting of two divine horses given to him as a gift from the sea god Poseidon and a famous horse he stole while assaulting a certain city, no one could chase after him from behind.
Hector was one of the greatest heroes in the Trojan War, being equal in strength and skill with Achilles, even when his weak point was exposed. Hector was the killer of Achilles' close friend Patroclus. Achilles, enraged with his friends death, challenged Hector in a one-on-one fight. Even after killing Hector, the way Achilles insulted him by dragging his corpse around with his chariot was a foolish and intolerable act. As a result, he incurred the displeasure of the sun god Apollo, but despite being repeatedly warned to restrain himself, Achilles continued slaughtering the Trojan army. So the enraged Apollo aided the Trojan army's bow expert Paris, and guided him to shoot Achilles' only weak point—that is, his heel. Having his heart pierced by arrows one after another afterwards, Achilles sensed his own death, but continued fiercely fighting and using all his strength to kill the soldiers of the Trojan army around him. Just as predicted, he had a short life, but his legend as a hero was carved into the world.