![large-e9b1ea8a2aee8fd902446d0c273f9eb4.jpeg](https://media.kitsu.io/anime/6028/poster_image/large-e9b1ea8a2aee8fd902446d0c273f9eb4.jpeg)
Assassin's identity is that of the legendary Persian "Old Man of the Mountain", Hassan-i-Sabah the leader of al-Assasīn. Assassin serves as the Servant of Kirei Kotomine in the 4th Holy Grail War, his unique trait being that he can manifest as multiple entities at once. (Source: Wikipedia)