Caster (キャスター, Kyasutā) is the Caster-class Servant of Ryuunosuke Uryuu in the Fourth Holy Grail War of Fate/Zero. Caster's True Name is Gilles de Rais (ジル・ド・レイ, Jiru do Rei), the version whose notoriety as "Bluebeard" (青髭, Aohige) normally overwhelms his heroic aspect.