Assassin (アサシン, Asashin) is the Assassin-class Servant of Kirei Kotomine in the Fourth Holy Grail War of Fate/Zero, and one of the Servants able to be summoned by the Protagonist of the Grand Order conflicts of Fate/Grand Order. He is unique in that he has the capability to manifest as multiple entities at once. Assassin's True Name is The Hundred-Faced Hassan (百の貌のハサン, Hyaku no Bō no Hasan), one of the nineteen people to hold the legendary Persian title of "Old Man of the Mountain" (山の翁, Yama no Okina), Hassan-i-Sabbah, the leader of al-Assasīn.