Salazar Slytherin (fl. c. 993—1000) was a pure-blood wizard, who lived in the early Middle Ages. Noted for his cunning and determination and regarded as one of the greatest wizards of the age (respectively as a Parselmouth and skilled Legilimens), Slytherin was one of the four founders of Hogwarts School of Witchcraft and Wizardry along with Godric Gryffindor, Helga Hufflepuff and Rowena Ravenclaw, as well as the namesake of the Slytherin House. Slytherin was "ancient and monkeyish."
He didn't trust Muggle-born students, and expressed his opinion by proposing that they should not be accepted at Hogwarts. However, when the other Hogwarts founders didn't agree, he left the school, never to return. Slytherin died sometime near the eleventh century, after creating the Chamber of Secrets, concealing a basilisk, ready to have the Chamber reopened to purge the school of Muggle-borns.