Caster of Black is the Caster-class Servant of Roche Frain Yggdmillennia of the Black Faction in the Great Holy Grail War of Fate/Apocrypha.
SpoilerHe also becomes the proxy Master of Berserker of Red after capturing him.SpoilerCaster's True Name is Avicebron (アヴィケブロン, Avikeburon), also known as Solomon ibn Gabirol (ソロモン・イブン・ガビーロール, Soromon ibun Gabīrōru), a twelfth-century poet and philosopher. He was born in Malaga, Spain, and although he did not have the glory of a knight or king or the recognition of having produced works of art that would prosper for thousands of years, he was the father of an entire thaumaturgical system, Kabbalah, and one of the starting points of the process leading up to the European Renaissance through bringing Greco-Arabic and Jewish lore and enlightenment to the cultural circles of Europe. He is recognized as a "hero" who heavily influenced both the history of the world and thaumaturgy.