True Assassin (Fate/stay night)

The True Assassin is an exceptionally dangerous Servant with a limited appearance in Fate/stay night and Fate/hollow ataraxia, but an expanded role in Fate/Zero. The designation of "True" is meant to distinguish this Assassin from another Servant that has usurped his place in the Fifth Grail War. All True Assassins share a collective identity and have appeared in every Holy Grail War throughout history. They are infamous for an ebony and tattered costume, as well as for concealing their identity behind an ashen skeletal mask.

Appearance
His appearance is that of a slender, dark man with his right arm bandaged. His right arm is described by Saber as useless flat board, incapable of doing much. His face, revealed by Sakura in the Heaven's Feel scenario, is that of a skull, without any skin. This inspires Sakura to say that he tries to live for eternity when he already lost his identity.

Abilities
He is able to conceal his presence, granted by his class as an Assassin. Unlike his improper counterpart, Epic Spirit labelled as Sasaki Kojirou, he is able to use this ability to a great extent, allowing him to watch over his enemy without revealing himself to other Servants, even Saber. He can also throw small, black daggers called Dark at his enemies, each one aimed at the enemy's weak point to ensure a kill. This, however, is practically useless to Saber and Lancer who holds abilities that enable them to dodge/parry projectiles thrown/shot at them. He also has protection against wind, saving him against an attack from Saber which she executed her Invisible Air. This ability seems to have originated from the time when he was alive, whereas he had to shield himself from sandstorms and similar events.

Assassin's Identity
True Assassin's identity is that of the legendary Persian "Old Man of the Mountain",, the leader of al-Assasīn.