An arrogant, selfish, and enigmatic Archer-class Servant. He appears familiar with Fuyuki City and claims to have a past relationship with Saber. Typically clad in an ornate golden armor, he possesses an immense number of Noble Phantasms, though none are representative of his true identity. Gilgamesh is the great half-god, half-human king born from the union between the King of Uruk, Lugalbanda, and goddess Rimat-Ninsun. He ruled the Sumerian city-state of Uruk, the capital city of ancient Mesopotamia in the B.C. era. He was an ultimate, transcendent being so divine as to be two thirds god and one third human, and no others in the world could match him. He was a despot possessing high divinity who believed he was invincible. He is not merely a legend, and is said to have actually existed and ruled during the Sumer Dynasty five thousand years ago. He was the King of Heroes who possessed all things in the world, whose tale is recorded in mankind's oldest epic poem, the Epic of Gilgamesh which portrays Gilgamesh as a hero, destined to be king and achieve great feats, who is driven to meet his destiny, facing challenges together with his best friend Enkidu. His title, King of Heroes, is not meant to call him a king who is a hero, but instead implies that he is the king over all heroes. He is mankind's oldest hero, the origin of all myths and model on which heroes are based, so his story is copied within the mythologies of all the countries of the world. The heroes of various myths are derived from his legend, so his Gate of Babylon possesses all of their Noble Phantasms. Though there are several heroes holding the title of "King," the King of Knights and King of Conquerors, he is the only one in all of heaven and earth crowned with the title of "King of All Heroes." In Fate/kaleid liner PRISMA☆ILLYA, he's the Heroic Spirit sealed into the eighth Class Card. He manifests as his younger self due to Illya separating him from his shadow form half-way through his incarnation. While initially an adversary, he quickly becomes an ally to fulfill his objectives. Gilgamesh in his child form has a more easygoing attitude compared to his adult self. He asks Illya to call him Gil-kun.

Rai is a very elegant and mysterious Noble. He has no knowledge whatsoever of the 21st century, and will often become lost and confused especially with regards to modern day technology (such as using a cell phone). He is often used as the manhwa's comic relief with his love of ramen and the errors he makes with technology. He has fallen into a deep slumber for 820 years, and had woken up in an abandoned building in South Korea. After seeing what most of the humans on the streets were wearing, Rai took on the uniform of a student from Ye Ran High School, which is under the administration of Frankenstein, and inadvertently followed the students there.