Slytherin or Salazar Slytherin was the founder of Slytherin house.
3 of the Hogwarts 4 co existed as friends 1 did not.
Salazar Slytherin wished for students to admitted to Hogwarts. He believed that magical learning should be kept in all magic families. Unable to persuay the other 3 he decided to leave Hogwarts and never come back. But before he left he built a chamber in Hogwarts and named it The Chamber of Secrets and he sealed it. (Until the time when his on true heir came to Hogwarts) The heir alone would be able to open the chamber and unleash a Basilisk!