Cú Chulainn (Caster) is a powerful Caster-class Servant from the Fate series, known as a top Servant whose name appears in fairy lore. Trained by the witch Scathach in the Land of Shadows, he mastered magic and martial arts, acquiring the iconic spear Gáe Bolg. In legends, he is depicted as a brave, benevolent young man who defeats enemies mercilessly on the battlefield yet upholds unbreakable oaths (Geis), valuing faith and integrity above all. Despite personal misfortunes, he endures with beast-like tenacity, fighting until the end even when mortally wounded, as reflected in tales of tying himself to a tree to battle on. He repays betrayal harshly but shows humor and maturity in alliances.