Caster (キャスター, Kyasutā?) is the Caster-class Servant of the Fuhrer in the Strange Tales of the Imperial Holy Grail of Fate/KOHA-ACE.
Caster's True Name is Maxwell's Demon (マックスウェルの悪魔, Makkusuweru no Akuma?), a fictional demon created by James Clerk Maxwell as a thought experiment, distorted by the desires of people.
Caster has short, well groomed orange hair, and is dressed in a Tan Business Suit with a Red Tie and Sunglasses.
Rather than being a magus, he is a scientist Heroic Spirit. Due to the nature of Maxwell's Demon not being resolved as of the 1940s, Caster is impossible to kill.