Salazar Slytherin

Salazar Slytherin is the posthumous overarching antagonist of the Harry Potter book and film franchise. He is one of the four founders of Hogwarts who founded the House of Slytherin and the ancestor of Lord Voldemort. Estranged from his fellow founders, Slytherin's goal was to purge Hogwarts from all Muggle-borns to keep the blood purity from Pure-blood wizards intact, directly influencing all the actions of Lord Voldemort and his Death Eaters hundreds of years later.