Gilgamesh begins as king of Uruk in ancient Mesopotamia, born from human king Lugalbanda and goddess Rimat-Ninsun. This heritage renders him two-thirds divine and one-third mortal. His birth served a purpose as the "Wedge of Heaven," destined to guide humanity away from divine rule as the Age of Gods faded. Initially a benevolent ruler in his youth, isolation born of his unique perspective—neither fully god nor man—twisted his reign into tyranny. He embraced oppression and decadence, drawing lament from his people and consternation from the gods. This path shifted when the gods dispatched Enkidu, fashioned from clay as the "Chains of Heaven," to temper his arrogance. After a battle lasting days outside Uruk's temple, the two acknowledged each other as equals and forged a profound friendship. Enkidu became Gilgamesh's sole confidant, guiding him back to his people and joining heroic quests like defeating the forest guardian Humbaba and the Bull of Heaven, unleashed by the spurned goddess Ishtar. Enkidu's death, decreed by the gods as punishment for slaying the Bull of Heaven, shattered Gilgamesh. Confronting mortality, he journeyed to the underworld seeking immortality. He obtained the Herb of Immortality only to lose it to a thieving serpent. This loss cemented his rejection of divine authority. Returning to a neglected and decaying Uruk, he dedicated himself to rebuilding it as a wise and just ruler. He established fortress cities, implemented governance through chief priest Siduri, and embraced his role as humanity's protector, symbolizing mankind's final separation from the gods. In conflicts like the Holy Grail Wars, he typically manifests as an Archer-class Servant, though he rejects formal class designations, demanding summoning by his true name. His personality embodies arrogance, proclaiming himself the "King of Heroes" who owns all treasures and noble phantasms as their origin. He scorns most humans as "mongrels," yet grants rare respect to figures like Iskandar or masters demonstrating unwavering resolve. Though ruthless—capable of killing displeasing masters—he rewards loyalty and values entertainment, permitting challenges from those he deems intriguing. His later incarnation as Caster reflects his post-immortality-quest wisdom. Here, he prioritizes Uruk's survival, foreseeing its destruction via clairvoyance and preparing defenses against the primordial goddess Tiamat. He summons other Servants, including Merlin, to fortify the city and sacrifices himself to buy time for Tiamat's defeat in the underworld. This period contrasts his typical self-centeredness, highlighting sacrificial leadership and commitment to human legacy. His relationships remain complex. Enkidu stands irreplaceable as his only friend, while he reacts with visceral disdain toward Ishtar due to her past actions. With masters, he evolves from indifference to mentorship, notably aiding Hakuno in Fate/EXTRA CCC by expending treasures for their survival. In lighter contexts like Fate/Grand Carnival, he participates in comedic segments addressing Servant labor issues, retaining his regal demeanor. His abilities center on the Gate of Babylon, a treasury holding every human invention's prototype, deployed as projectile weapons. His ultimate noble phantasm, Enuma Elish, wields the sword Ea to rend space. As a Servant, he possesses near-omniscient foresight (Sha Naqba Imuru), though he selectively ignores this knowledge to preserve amusement.