Pegasus Seiya (Japanese: 天馬星座(ペガサス)の星矢, Hepburn: Pegasasu no Seiya), also known as Seiya, is the titular character and main protagonist in the Saint Seiya manga and anime series, created by Masami Kurumada. He debuted in the first chapter "The Saints of Athena" (女神（アテナ）の聖闘士, Atena no Seinto), published in Weekly Shōnen Jump on December 12, 1985. Seiya is one of the eighty-eight Saints, mythical warriors who have served the goddess Athena and protected Earth throughout the ages, though he is initially only interested in finding his missing older sister, Seika. He eventually becomes one of the twelve strongest Saints, the Gold Saint Sagittarius Seiya (射手座サジタリアスの星矢, Sajitariasu no Seiya), while personally assisting Athena's reincarnation, Saori Kido. Seiya is the successor of Sagittarius Aiolos, the previous wielder of his Gold Cloth, who often sends his protection even before Seiya becomes a Gold Saint. As a Saint, Seiya dons a Cloth, an armor of divine origin, with his Cloth representing the constellation of Pegasus, and possesses superhuman strength and speed, which are among the abilities the Saints draw from their guardian constellations and the inner essence of Cosmo. Seiya has also appeared as a main supporting character in other works related to Saint Seiya, such as the anime Saint Seiya Omega and the Saint Seiya Episode.G manga trilogy.

Seiya's design was inspired by Ryuji Takane, the protagonist of Kurumada's manga Ring ni Kakero. He was originally voiced by Tōru Furuya in the anime series and films before being replaced by Masakazu Morita.

Kurumada originally planned to create a manga about wrestling, as he enjoyed writing about individual sports rather than collective sports. He was initially inspired by The Karate Kid (1984) to create a story about Seiya, a young karateka who is found by a karate master and his female assistant; however, his publishing department did not approve the idea. While creating Saint Seiya, which he originally titled Ginga no Rin (銀河の輪, "Rin of the Galaxy"), Kurumada initially gave Seiya the name Rin. However, as he developed the story, he changed his name to Seiya, which he felt was more fitting. Seiya's name was originally written with the kanji for "holy arrow" (聖矢, seiya), relating to his position as a Saint, but he later decided to write it with the kanji for "star arrow", to emphasize the constellation and mythological motif. He also changed the title of the manga to Saint Seiya once the concept of the Saints was fully developed. Kurumada stated that one of the first ideas he had for Saint Seiya was the "Pegasus Meteor Fist". Since the manga was going to use the constellations as a recurring theme, he wanted his protagonist to have a special move that would be like a shower of meteors. Along with Hyoga's Cygnus, Pegasus was chosen as Seiya's constellation from the beginning, with the series later expanding on the twelve signs of the zodiac. Kurumada recalled that, as in some of his previous works, the main characters were less popular compared to the supporting cast.

Seiya's likeness was inspired by Ryuji Takane, the protagonist of Kurumada's manga Ring ni Kakero, which he considers to be his favorite creation. Most protagonists in his works bear a resemblance to Ryuji because Kurumada subscribes to Osamu Tezuka's Star System: the principle of maintaining a stable cast of characters who play different or similar roles in an author's works, which was used to create most characters in the series. The Sagittarius Gold Cloth was chosen as the most famous of the Gold Cloths because of its symbolism in relation to Seiya. He felt that Seiya's name was a perfect match for him, as the Japanese meaning of his name, "star arrow", is a metaphor for "meteor" and Sagittarius represents an archer, especially since he had in mind that Seiya would eventually wear the Sagittarius Gold Cloth. As such, Seiya's zodiacal sign is Sagittarius. Seiya's God Cloth was specifically created to defeat the God Thanatos, though Kurumada felt that he exaggerated this in retrospect.

In the animated adaptations of the series, Seiya was voiced by several voice actors. Tōru Furuya voiced him in the 1986 anime series, all five theatrical releases, the first series of original video animations (OVA) adapting the Hades arc of the original manga, released in 2004, and the 2012 anime series Saint Seiya Omega. Hiroko Emori provided additional voice acting for scenes in which Seiya appears as a child. In the Hades arc OVAs, released from 2005 to 2008, Seiya was voiced by Masakazu Morita. In the uncensored ADV English dub, he was voiced by Illich Guardiola and Cameron Bautsch, and by Tim Hamaguchi in the censored dub by DiC Entertainment. He is voiced by Bryson Baugus in the CG Knights of the Zodiac and the Netflix dub. In the Latin American dub, he was voiced by Jesús Barrero.

Furuya stated that Seiya was his favorite character out of all his voice roles and laughed when performing his "Pegasus Meteor Fist". Morita stated that Seiya was one of his favorite characters due to how "passionate" he is. Kaito Ishikawa stated that he was happy with the work he was assigned to for Legend of Sanctuary.

Seiya is the titular character and main protagonist of Saint Seiya and one of the eighty-eight Saints who serve Athena. Seiya draws his superhuman powers from the Cosmos, the energy of the Big Bang that is present in all living things and connects a Saint to his constellation and Cloth. At the start of the series, Seiya is thirteen years old. His main goal is to find his older sister, Seika, who disappeared when he was sent to Greece to train to become a Saint under the Silver Saint Eagle Marin. Due to her physical similarities to Seika, Seiya suspects that Marin may be his sister, but is proven wrong after he finds Seika. As Seiya begins fighting alongside the other Bronze Saints, albeit reluctantly at first, his motivations shift to protecting Athena. Although passionate and brave, he can be brash and impulsive at times. Despite this, he is kind-hearted and selfless, willing to risk or sacrifice himself for justice, his friends, and Athena. His most notable trait is his determination and refusal to give up, even against the odds. He also has a habit of making jokes and can be unconcerned about the consequences of his actions.

Seiya is a teenager who is sent to Greece to train under Marin and obtain the Pegasus Bronze Cloth before returning to his home in Japan. There, he discovers that his older sister Seika has gone missing. Saori Kido negotiates with him to fight other people who have become Saints to attract the media's attention and have her group search for Seika. However, his former companion Phoenix Ikki, who seeks revenge for the training he went through, confronts him. Although Seiya defeats Ikki with help from his friends, the Sanctuary's Pope sends the Silver Saints to attack them. After learning that Saori is really the reincarnation of Athena, the Saints head to the Sanctuary and through its Twelve Temples before confronting the tyrant Pope, during which Saori is mortally wounded. Although Seiya begins as a Bronze Saint, over time his abilities grow to rival those of the Gold Saints as he awakens his Seventh Sense, the essence and origin of the Cosmo. After mastering the Cosmos known as Seventh Sense, Seiya and his friends defeat the strongest Gold Saints, including the Pope, who is revealed to be Gemini Saga, and save Saori.