Caster (キャスター, Kyasutā) is the Caster-class Servant of Souichirou Kuzuki in the Fifth Holy Grail War of Fate/stay night. She also acts as the Master of another Servant, Assassin. Caster's True Name is Medea (メデイア, Medeia), an unfortunate princess who was labeled as a witch in Greek mythology. She was the princess of Colchis who possessed the Golden Fleece. Her father, King Aeëtes of Colchis, excelled at magic, and as his daughter, she was also practiced in such ways.