Avenger (Angra Mainyu)

Avenger (アヴェンジャー, ?) is the Avenger-class Servant of the Einzbern family in the Third Holy Grail War. He is an abnormal Servant that is not part of the regular seven classes, whose true identity is Angra Mainyu. While he was not actually the evil god of Zoroastrianism, his defeat in the Third War corrupted the Grail, turning it into the equivalent of All the World's Evils. This manifestation attempts to be born through the Holy Grail, and acts as the Servant of Sakura Matou in the Fifth Holy Grail War of the Heaven's Feel route of Fate/stay night. He acts as the Servant of Bazett Fraga McRemitz in place of Lancer in the four day loop of Fate/hollow ataraxia.
Avenger was initially believed to be the Persian god of darkness, Angra Mainyu. In reality, he was no more than an ordinary villager. A human that was freed from the confines of Order by having his name expelled from the Avesta, The Universal Revelation of Inscribed Creation. One day, he was randomly chosen as the "source of all evil in the world" by his village and was tortured and sacrificed in the following rituals. The villagers believed that from the moment humans are born, there is evil in them. Since it was impossible to be freed from malice just through clean, righteous living, the only way to realize the true goodness of human beings was to force "all the evils of the world" onto one person and blame him as the true source of any human evil. If one person embodies all the evils of the world, the rest of the people cannot be evil, no matter what. This was the simple, child-like theory they all invested in.