Salazar Slytherin
Professor Salazar Slytherin was a pure-blood wizard of medieval times. He was a Parselmouth (a wizard with the rare ability to speak with snakes), and skilled at Legilimency. He was one of the four founders of Hogwarts School of Witchcraft and Wizardry and the former best friend of Godric Gryffindor, a fellow founder. Slytherin didn't trust Muggle-born students due to him being reminded of the persecution against wizards by Muggles, and he expressed his opinion not to accept them at Hogwarts. However, when the other Hogwarts founders didn't agree, Slytherin left the school and did not return again, but not before creating the Chamber of Secrets and concealing a basilisk inside. He died sometime in the middle ages