Pegasus Seiya is the protagonist of the anime and manga series Saint Seiya, which is also known as Knights of the Zodiac. He is a Bronze Saint of the Pegasus constellation, one of the eighty-eight legendary warriors who serve the goddess Athena and protect the Earth. Seiya is introduced at the age of thirteen, having been separated from his older sister Seika during childhood and sent to Greece as an orphan. There he spent six years training under the Silver Saint Eagle Marin, enduring grueling conditions before earning the Pegasus Bronze Cloth by defeating ten other trainees in a brutal competition. His early life is defined by this separation, and his first major motivation is simply to be reunited with his sister.

In terms of personality, Seiya is passionate, brave, and fiercely loyal. He is often described as impulsive, brash, and quick to act, with a tendency to speak his mind and make jokes even in tense situations, which can make him appear cheeky or insolent at first glance. Beneath this outward behavior, he is kind-hearted and selfless, willing to put his own life at risk for the sake of his friends, innocent people, and the goddess he serves. His defining trait is an absolute refusal to give up, no matter how dire or hopeless a battle appears. This stubborn determination, combined with his courage and willingness to sacrifice himself, is what allows him to overcome opponents far stronger than himself.

His motivations evolve significantly over the course of the story. Initially, Seiya is reluctant to involve himself in larger conflicts and is driven mostly by the personal goal of finding Seika. When Saori Kido offers to help search for his missing sister in exchange for his participation in a fighting tournament, he accepts, and this decision draws him into a much larger war. As he fights alongside the other Bronze Saints and learns the truth about Saori, who is the reincarnation of the goddess Athena, his motivation shifts from personal gain to a genuine commitment to protect Athena and fight for justice. His devotion to Saori becomes one of the central emotional anchors of his character, and much of his journey is defined by his readiness to throw himself into danger to save her.

In the story, Seiya functions as the main protagonist and a natural leader among the five central Bronze Saints. He plays a decisive role in the Sanctuary conflict, where the Saints must expose a false leader who has seized control of Athena's forces, and then in the war against Poseidon, the god of the seas, who threatens to flood the world. His greatest trial comes in the battle against Hades, the god of the underworld, where the Saints face the forces of the dead. Throughout these arcs, Seiya repeatedly surpasses his limits, awakening the Seventh Sense, a higher level of Cosmo awareness that allows Bronze Saints to fight on equal footing with the vastly more powerful Gold Saints. At key moments, he wears the Sagittarius Gold Cloth, inheriting the legacy of the Gold Saint Aiolos, who protected Athena as an infant and whose spirit continues to watch over Seiya. He is recognized as the future successor of Sagittarius, and in later stories such as Saint Seiya Omega, he becomes a Gold Saint and a mentor to a new generation of warriors. By the end of the original conflict, Seiya manages to defeat the gods Poseidon and Hades, but he is struck by Hades' sword and left cursed, with his soul unable to reincarnate again. This leaves him in a comatose state, and Athena's efforts to save him are the starting point of the sequel story Saint Seiya: Next Dimension.

Seiya's key relationships are central to his character. His bond with Saori Kido, Athena's mortal form, evolves from a strained and transactional arrangement into deep loyalty and devotion, and she becomes the person he is most determined to protect. His relationship with his sister Seika is the emotional foundation of his early journey, and his suspicions that his master Marin might be Seika due to their physical resemblance add a personal layer to his training years. Among his fellow Bronze Saints, Seiya forms strong bonds of friendship with Dragon Shiryu, Cygnus Hyoga, and Andromeda Shun, as well as with Phoenix Ikki, a former rival who becomes a trusted ally. These warriors repeatedly risk their lives for one another, and their camaraderie is one of the defining themes of the series. Seiya also has a complicated connection with the female Saint Shaina of Ophiuchus, who is bound by tradition to either kill the man who has seen her face or love him, and he is defended at one point by Cassius, a rival from his training days who sacrifices himself to save him. The protective influence of Aiolos, whose Cloth and will aid Seiya at crucial moments, also shapes his role as the future Sagittarius Saint.

As a warrior, Seiya draws his power from the Cosmos, the internal energy present in all living things that originates from the Big Bang and connects a Saint to their guardian constellation and Cloth. His abilities include superhuman strength, speed, agility, and reflexes far beyond normal human limits. His signature technique is the Pegasus Meteor Fist, a devastating barrage of punches so fast and numerous that it resembles a shower of meteors. He also uses the Pegasus Comet Fist, a more concentrated and powerful variation. Unlike some of his comrades, who rely on elemental or specialized attacks, Seiya's fighting style is grounded in raw speed, relentless offense, and an unshakable will. His Pegasus Cloth is a divine suit of armor tied to the constellation of Pegasus, providing protection and amplifying his combat ability. Over time, the Cloth is repeatedly damaged and restored by the Gold Saint Aries Mu, and after being bathed in the blood of Gold Saints, it gains enhanced power, changing color and even developing wings in the battle against Hades. In the final confrontations, Seiya also manifests the God Cloth, a legendary form of armor created specifically to stand against divine beings, which enables him to fight the gods themselves. His growth as a character is closely tied to these escalating powers, but his ultimate strength lies in his refusal to abandon hope or his companions, even when facing gods who command the forces of nature and the afterlife.