Caster (Fate/Zero)

Caster is a character from the Fate/Zero.

He is the Servant of Uryuu Ryuunosuke during the 4th Holy Grail War. Caster derives pleasure from first providing his victims with a moment of relief and hope, before killing them in a variety of horrific manners.

True Identity
His true identity is, a French nobleman who was once a comrade-in-arms of. He first introduces himself to his Master as, which is the name of a fictional character based on Gille himself.

Role
Caster was summoned shortly before the Fourth Holy Grail War began. His Master was Ryūnosuke Uryū, a serial killer who unwittingly performed a successful summoning ritual using the blood of a murdered family. Like his Master, he is almost devoid of any morality, and has no interest in obtaining the Holy Grail. He enjoys offering his victims brief moments of respite, or even the hope of release or escape, before inflicting death through gruesome and horrific means. According to Caster, allowing his victims hope will amplify the despair and terror upon their moment of death, a fact that he revels in. He also uses his magic to warp and twist humans into contraptions for his Master's entertainment, such as turning a girl into a pipe organ.

Caster initially expresses an interest in Saber, appearing to be familiar with how she came to ruin at the end of her life. In truth, it is because he has mistaken her for Jeanne D'Arc, whom he had been infatuated with when alive. Even after Saber reveals her true identity, Caster continues to delude himself, believing that her memories were warped by the trauma of her death. He even makes plans to capture Saber and force her to remember her 'true' past.

It soon comes to the attention of Kotomine Risei, the Holy Grail War's regulator, that Caster is kidnapping children throughout Fuyuki (for use in his spells and for his Master's amusement), and that he and Uryū lack the discretion practiced by the other Master-Servant pairs. Fearing their actions might compromise Tohsaka Tokiomi's chances of winning the War, Risei suspends all fighting and offers a reward of extra Command Spells to the Master who dispatches Caster and Uryuu.

Using the captured children as hostages, Caster draws Saber out and traps her in battle with his seemingly infinite army of summoned monsters. He is defeated when Lancer intervenes, breaking through the monster horde with Saber's aid, and using Gáe Dearg to disable Prelati's Spellbook and dispel the summoned creatures. An enraged Caster then retreats.

In his second bid to capture Saber, Caster merges a horde of his monsters into an immense, Lovecraftian beast, with himself at its centre. Despite its vast strength and regenerative powers, it is ultimately defeated by Saber, who incinerates the beast with her anti-fortress Noble Phantasm, Excalibur. The light from Excalibur's blast causes Caster to recall a memories from his past, before he began his forays into murder and the occult, back when he still served alongside Jeanne D'Arc. This evokes tears and a tinge of regret in Caster, moments before he is destroyed along with his monster.