Assassin (Fate/Zero)

Assassin is the Servant of Kotomine Kirei in the 4th Holy Grail War, his unique trait being that he can manifest as multiple entities at once.

Abilities
Unlike True Assassin, who was one entity, Assassin existed as nearly one hundred separate entities. His multiple bodies were the result of the original Hassan-i-Sabah intentionally fragmenting his psyche in life, a sort of self-inflicted dissociative identity disorder, to compartmentalize the various skill sets and knowledge he had accumulated during his lifetime. As a Servant, these multiple personalities are expressed in the form of multiple bodies, one for each distinct personality. Each personality in turn took on its own independent body as a Servant, with individual tasks relegated to the personality best suited for it.

True Identity
As with every Assassin, his identity is that of the legendary Persian "Old Man of the Mountain", Hassan-i-Sabah the leader of al-Assasīn.

Role
The Assassins initially act as reconnaissance agents for Tokiomi and Kirei, after Gilgamesh "kills" one of them in full view of the other Masters. This tactic successfully lead most of the Masters to believe that Kirei and Assassin had been defeated, and allowed the dozens of remaining Assassins to move freely without suspicion. Their continued existence, however, is discovered when Rider and Waver Velvet accidentally encounter three Assassins in Caster's lair.

The Assassins meet their end when they are sent to gauge Iskander's power levels. He complies by using his most powerful Noble Phantasm, "Ionioi Hetairoi: Army of the King", to massacre each and every one of the Assassins.