Although not a Servant, he is an immortal with a legend comparable to one. He is the man known as the Wandering Jew, punished for ridiculing Jesus by being forced to wander until the Last Judgment. By the time of Fate/Requiem he is the oldest human alive, a man who has had an even longer lifespan than Noah or Methuselah.
Ahasuerus is a loud and lighthearted man who enjoys laughing and cracking jokes even if no one else responds. According to him the only time he'll ever be quiet is the day when he'll die and meet the Buddha - saying this despite being Jewish, not Buddhist. He is crude and irreverent, but truly respects the desires of his Servant Hendrik van der Decken. He believes that there is no true place of rest in the whole world, and hates when he sees naivety in people.
Ahasuerus and his Servant Hendrik had made port at the Akihabara Ward of Mosaic City. Hunted by Kundry who deems Hendrik her lover, Erice Utsumi escorts the Master-Servant pair to the docks for them to make their escape.
Having made their way to sea, Decken summons his legendary ship, the Flying Dutchman at the behest of Ahasuerus' Command Spells which promptly destroys Kundry's gremlins before leaving the city for good.
- Fate/Requiem Volume 1: The Boy Among the Stars - Prologue