berserker

 class: Berserker
 real name: Hercules (or Herakles)
 measurements: 253cm (height), 311kg (weight).
 colour: lead.
 natural enemies: Gilgamesh.
 likes: Ilya.
 dislikes: Ilya's enemies.
 master: Ilya.
 weapon: his own strenght, a huge stone blade.
standing: Chaotic mad.
noble phantasms: Berseker only has a noble phantasm, which is anyway enough.
- God Hand - The Twelve Trials (he can be resurrected, through his half-divinity nature, for eleven times for a total of 12 lives, as the fatigues of his legend).

personality: I can't tell you very much about Berseker, since as his class suggest he's almost always "mad". He only cares about fighting and protecting his Master, no matter what. He's very devoted and Ilya sometimes associates him as a paternal figure. Berserker seems to be not interested or even not able to understand what's going on in the Grail War, maybe because he's always in his rage "mode". Anyway he's more conscious about the situation than most of the other characters involved. His reasons are still a mistery, but peraphs, being one of the most symbolic heroes of all the times, he doesn't really need a reason to fight, except than his own will.

spoilers warning!!!

personal history: Berserker is summoned by the young Ilya, and despite the difficulties in controlling such a Servant (for his class mainly), she's able to command him pretty well. Berserker follows her orders and does everything he can for her as it also seems there's a strong bond between them, something that doesn't really relates to the Grail War.
In the first scenario Berserker is guarding Ilya's castle and with his powers he's able to defeat Archer (although he's killed many times) but he's eventually beaten by Saber and Shirou with the support of Rin, as Ilya and him are after them as they were trying to escape from the forest surrounding her palace. In Unlimited Blade Works he's defeated by Gilgamesh soon in the story and he leaves Ilya to Shirou, as he knows he could look after her. In the third scenario he's eaten by the shadow and turned into Black Berserker, a less powerful (and also blind) version of himself.
Finally in Hollow Ataraxia he's still featured as Ilya's servant (even if he's considered as a sort of ghost) although he doesn't appear much and he has a very secondary role.

the legend behind: Hercules (also known as Herakles) is one of the most famour characters of the greek and roman myths. He's the son of Alcmena and Zeus, a demi-god who was hated from his birth by Hera and pursued by her since he was a child. She sent two snakes in order to kill him as he still was a baby, but thanks to his incredible strenght he was able to choke both them with his hands. He is mostly well-known for his 12 trials, a sort of punishment given to him by Eurystheus for the murders he commited (he went mad and killed his wife and his sons).
In the first one he killed the lion of Nemea with his own hands; in the second one he chased and killed the Hydra of Lerna who was able to regenerate its three heads; the third one consisted in to hunting and bring back to Eurystheu the great boar living on Mount Erymanthus in Arcadia. The fourth one was to capture the Cerynitis a sacred animal of Artemis living on Mount Cerynaea, and he had to wander for a whole year before finding him and being successful.
The fifth trial was the one to eliminate the birds living around Lake Stymphalus; the following one was to clean the Augean stables in one day (something incredible considering those stables were enormous); the seventh trial was to capture a bull, made mad by Poseidon, who was terrorizing Crete: The eight fatigue was to was to bring back to Eurystheus the savage mares of Diomedes, the ninth one was to retrieve the girdle of Hippolyte of the Amazons. After that trial he had to bring back to Eurystheus the cattle of Geryon and later to retrieve three of the golden apples guarded by the Hesperides. Finally he had to capture alive the guard dog of the Underworld: Cerberus.
After the trials Heracles wandered around the world. He fell in love with Iole, daughetr of the king of Tessaglia, but as he coudln't marry her, he killed her brother. In order to cleanse himself for this murder he was sold to queen Onfale of Lidia.
Later on he was able to conquer Troy and kill his king. After that he went to Etolia and he met Deianira who married him and led him to his destruction. As he tries to commit suicide, Nike sent by Athena, is able to rescue and purify his body and he's accepted inthe Olympus where he would spend the rest of his eternal existence.