Gilgamesh

Gilgamesh is the King of Uruk, said to have reigned during the Sumer Dynasty in Mesopotamia 5000 years ago. He's the namesake Hero described in the Epic of Gilgamesh, making him the most ancient Hero on which all the others legends were modeled. This grants him the title of King of Heroes and, within his Gates of Babylon, the prototypes of all the Noble Phantasms of the Heroes yet to come.

Born from the human Lugalbanda, the King of Uruk, and the goddess Rimat-Ninsun, he was a being so perfect and transcendent to the point that he was two-thirds deity and one-third human. He was the chosen one that would guide humanity on the earth that was slowly abandoning the Age of Gods, but instead he grew up to be a selfish and arrogant despot.

His only friend and being he considered his equal was Enkidu.

In Fate/Zero:
Initially summoned as the Archer-class Servant of Tokiomi Toosaka in the 4th Holy Grail War, using the fossil of the first skin ever shed by a snake as a catalyst, he soon becomes bored with his Master and takes interest in Kirei Kotomine. Together they plot to kill Tokiomi and forge a new pact, with Gilgamesh pushing Kotomine to accept his true desires. He also takes interest in Iskandar as a worthy opponent to kill, and in Artoria, a tragic figure to take as his bride.

In the end, invested by the pollution of the Holy Grail, he is gifted a mortal body and is reincarnated in the world.

In Fate/strange Fake:
Within the World of Fate/strange Fake, Servant Archer Gilgamesh was previously summoned in the Fourth Fuyuki Holy Grail War and participated in the Fifth Fuyuki Holy Grail War. But the Servant summoned in the False Holy Grail War is a new Servant without any memories of the Fuyuki Holy Grail Wars.

He is the first Servant summoned in the True and False Holy Grail War as the "False" Archer-class Servant of Thine Chelc.