Idk he seems kinda evil and JK Rowling puts every evil person in Slytherin .

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Ravenclaw seems correct. However, immanentizing the eschaton is usually signature bad guy. Sorting him into Ravenclaw rather than Slytherin requires recognizing that the telos of Christianity and its opposite are orthogonal to the questions of amoral dominance vs righteousness represented by the Slytherin/Griffindor rivalry. Ravenclaw is only the most proximate point on an entirely different map.