For the three or four of you who are unfamiliar with Professor Snape, we’ll give you a quick and dirty lowdown. Imagine the teacher who always had it out for you, the one who was quickest to point out how stupid you were and slowest to see the faults of others. Now put that teacher in a greasy black wig and a long black dress and give him the power to do black magic.

There’s a reason we asked you to imagine a specific teacher. Because that’s exactly what J.K. Rowling did when she created the second-greatest villain of the Harry Potter series. And the teacher she pictured was her own secondary school chemistry master, John Nettleship.

In retrospect, Nettleship described himself as “a short-tempered chemistry teacher with long hair … [and a] gloomy, malodorous laboratory” who enjoyed picking on students, particularly bright students like Rowling. Which was why it was kind of weird that it took reporters straight up asking him if he was Snape before he figured it out. Even his wife knew the connection, but, tellingly, was too scared to bring it up.

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