Eighth servant class appearing in Fate/hollow ataraxia.
True Name: Angra Mainyu
Major antagonist in the Fate series. He participated in the Third Holy Grail War but was defeated. The Holy Grail became corrupted as a result, turning it into the equivalent of All the World's Evils.
- Type-Moon wiki (spoilers): http://typemoon.wikia.com/wiki/Avenger_(Fate%2Fhollow_ataraxia).