Caster (Fate/Zero)

"My only wish was that the holy maiden Jeanne d'Arc would be resurrected, and now this wish had already been fulfilled! Without even the need to compete with anyone, my wish had already become reality!"

- Caster, Fate/Zero

Caster is a villain from Fate/Zero who is the servant of Ryuunosuke Uryuu during the fourth Holy Grail War. Caster derives pleasure from providing his victims with a moment of relief and hope before murdering them in horriffic manners.

Identity
His true identity is Gilles de Rais, also known as Bluebeard, who was a French nobleman who was once a comrade-in-arms of Joan of Arc. He remembered the time that he and Jeanne were decorated as saviors by King Charles in the cathedral with the ars nova playing in the background. In his lifetime, he admired Jeanne so deeply that he was devastated when she died, leading his faith in God to change greatly as he thought God had abandoned Jeanne. He began studying the dark arts under François Prelati, eventually receiving his own spellbook.

He began causing atrocities that he continued for 8 years until the Church and State caught him, seizing his wealth and land, after which he was executed for his crimes. After his death, he was removed from the cycle of transmigration and became a legendary spirit. He first introduces himself as Bluebeard, a name taken from a fictional character based on Gilles himself - a mass serial children murderer - to his Master, Ryuunosuke.

Personality
Just like his equally murderous Master, Ryuunosuke, Caster is almost utterly devoid of any morality, and has no interest in obtaining the Holy Grail. He loves to offer his victims with brief moments of respite, or even the hope of release or escape, before causing them death through whatever horriffic and gruesome means possible. According to himself, allowing his victims hope will amplify the despair and terror at the moment of their death, a fact that he himself delights in.