No, Snape was not a real person. However, the character of Severus Snape is said to be loosely based on Rowling's chemistry teacher John Nettleship. Snape might also be based on several other teachers that Rowling encountered in her childhood. Another teacher named Mrs. Morgan who J.K. Rowling had as a math teacher could also be a partial inspiration for the character of Snape as she was really strict.