Slytherin was one of the four co-founders of the Hogwarts School of Witchcraft and Wizardry. Contrary to the beliefs of his peers, Slytherin believed the school should employ a stricter policy of admittance. He believed that only children of magical ancestry should have permission to attend the school. Because of controversy with the other founders, he left the school. Before he left, he built an underground lair known as the Chamber of Secrets.