「Please gentlemen, let me borrow your hands. Everyone's convenient villain has entered the stage, so let's us please give him a magnificent welcoming--- or so, ehehehehehe!」
Zoroastrianism, regarded as mankind's oldest good and evil dualism doctrine. A Servant crowned with the name of the devil king transmitted in said Zoroastrianism. Only the summoner can judge whatever he is the true Angra Mainyu or not. A Heroic Spirit specialized in killing humans, but he can't do anything other than that. In the Holy Grail War, a place of battle for super-humans, he is of no use whatsoever. The weakest Servant, in both name and reality.