gilgamesh

 class: Archer
 real name: Gilgamesh
 measurements: 182cm (height), 68kg (weight).
 colour: gold.
 natural enemies: Archer.
 likes: being rich, getting richer, conquering the world, strong women (especially Saber)
 dislikes: his same ambitions
 master: Kotomine Kirei
 weapon: Air (Sword of Destruction, able to break the world apart), Bull of Heaven Chain.
standing: Chaotic good.
noble phantasms: Gilgamesh has powerful noble phantasm (and he could have even more considering who he is).
Enuma Elishi - The Star of Creation that Breaks Apart the Heaven and Earth (tecnique possible through the usage of Air, that creates a space and time distortion able to majorly damage or destroy those included in it).
Gate of Babylon - The King's Treasure (immaginary key that leads to the legendary town, letting him get all the items he keeps in his treasure room).
Erukidu (the Chain that governs gods, a powerful weapon that hits divinities according to their nature).

personality: Gilgamesh is mad, or at least he acts as he doesn't really understands his own actions (but he isn’t probably that insane). On one side he wants to get even more power than the one he already got, on the other side he pities himself (and that's probably because of his natural undecision that e keeps loosing at decisive stages). He's a powerful servant although he doesn't respect that much his Master and he hasn't of course an high opinion of him (probably because he kept him imprisoned for a long time). He would love to get the control of the other Servants for himself, especially of Saber who's one of the thoughest opponent he ever found in his way, and probably the woman who incarnates his feminine ideals after all, since he proposes to her more than once. Since he has always been a king, he doesn’t have any friendly approaches with anyone, and I don’t really think he likes to follow the order of a master, whoever could be.
We don’t really know the reasons why he joined the war. He’s probably lead by his own pride, by his will to become even more powerful than he already is, or peraphs he’s still looking for the secret of immortality (and that’s probably why he wants to get the Grail for himself). He probably feels a deep lonelyness but being semi-divine he doesn’t want to show some “human sides” like emotions or feelings.

spoilers warning!!!

personal history: King among Heroes, Gilgamesh was a servant of the previous War, Kotomine Kirei servant to be exact. He couldn't win the war because of the sudden events that destroied the Grail and he's summoned back in the present time., although we can't properly say it, since it seems he has never disappeared from this world. Kotomine Kirei mantained him in the present time, although the war was already finished, through the energy furnished by the orphans he collected after the destruction of the town. He supplied Gilgamesh with their energies, keeping him hided in his church. He is a though opponent for Shirou and his friends, as he's always hiding himself till the very end, when he can take advantage of the situation (and the fact that everybody else is tired by the conflict). In the Fate scenario, as well as in the anime, he's a dangerous threat for Saber and Shirou, especially for the servant, representing her final enemy and entertaining himself with a furious battle, till the very end of the war.
Gilgamesh badly wants to be victorious but he's defeated by Saber and her Excalibur and being defeated he vanishes for good. In the second scenario Gilgamesh is even more dangerous as he also represents a menace to Ilya and Berserker, being able to defeat them withouth any problem. In this scenario he has to face Shirou as his final adversary and he's beaten by his Unlimited Blade Works. In the third scenario, due to the introduction of different main "villains" his role is less important or striking and he ends up in being prematurely defeated and eaten by the tainted Grail, as well as most of the other servants.
We also see him in Hollow Ataraxia as part of the group of the main characters. Anyway he mainly appears in a younger version, since he doesn't really enjoy the company of the other characters and, drinking a potion, he can switch to a younger self (who is anyway more sociable and more respectful than his adult form). He doesn't play a striking role here as well, but he has some nice side interactions.

the legend behind: Gilgamesh is the mythical King of the Sumerian, who reigned in the town of Uruk. He was more divine than human and he was well-known for the cruelty of his government. He wanted all the young warriors to hardly train to become perfect soldiers, creating a sort of hate in his regards by everyone, at least until he meets Enkidu, a mysterious and savane creature made by the gods, whom he can’t defeat despite his great skills in combat. Gilgamesh and Enkidu make a friendship pact and they decide to go out the town for a quest, or well cutting some trees and bringing back those most beautiful and valuable, which leads them in a particular forest guarded by the monster Hubaba. As they enter in the garen they are immediately caught by the monster but they’re able to defeat him and come back to Uruk successfully.
Gilgamesh offers the prize to the goddess Ishtar who, noticing his courage and beauty, decides to propose herself as his spouse, but the king refuses (as he knows Ishtar is used to love someone only for a short time and she’s always able to condamn the abandoned husband if she wishes to punish him). Ishtar, who is offended by Gilgamesh asks to her father Anu to entrust her the Bull of Heaven and she sends the beast through the streets of Uruk, letting it kill and destroy everything in its way.
Enkidu fights twice against the bull, at first alone, and later with the help of Gilgamesh who kills it by stapping it on its head, between its horns. The two heroes win, strong of their valor. Anyway Enkidu dies because of the will of the gods and Gilgamesh feels lonelyness and desperation for the first time in his whole life. He realizes he can’t let Enkidu leave him and he decide sto look for the man who knows the secret of immortalità Utnapishtim, the ancient king of Shuruppak, one of his ancestors.
Anyway as Gilgamesh finds him in Dilmun (the land in which the sun rises) he realizes he doesn’t own any secret and that the king become immortal due to some circumstances that can’t be repeated. The man gives him a suggestion, or well tells him to find a legendary erb, called “old back to youth” (Nd: a rough translation, please tell me the correct name in english if you know it). Gilgamesh wills to bring it to his people and looks for it through the lands. He’s able to find it but as he falls asleep a snake steals it and eats it, and as a consequence of its acts it changes its skin, making impossibile to Gilgamesh to catch it and take his own avenge.