Severus Snape era baseado em uma pessoa real?

Aparentemente, a resposta é simples e não é surpreendente:

Professor de química de JK Rowling.

De este artigo sobre John Nettleship , que morreu de câncer em 2011 aos 71 anos:

"The first I knew was when a reporter from a national newspaper knocked on the door seven years ago and said: 'You're Professor Snape aren't you'," said the former head of science.

"I suppose I was quite strict as a teacher, but I said to my wife, 'she thinks I'm Professor Snape'. She said 'of course you are, but I didn't want to tell you'.

"Fortunately for me, quite a lot of people like Alan Rickman, who plays Snape in the films."

E ele se parece um pouco com Alan Rickman, menos a cortina de cabelos escuros:

A conexão foi mais ou menos confirmada por JKR, que disse (ênfase meu):

OK. Snape is the - er - very sadistic teacher loosely based on a teacher I myself had, I have to say. Erm .. I think it ... Children are very aware - and we ... we're kidding ourselves if we don't think that they are - that teachers do sometimes abuse their power and this particular teacher does abuse his power. He is not a - he is not a particularly pleasant person at all. However, everyone should keep their eye on Snape, I'll just say that, because there's more to him than meets the eye, and you will find out part of what I'm talking about if you read book four.

Esta citação diz que Snape foi definitivamente baseado em um dos professores de JKR. Um professor de química faria sentido (química ~ Poções), e juntamente com as citações acima sobre John Nettleship e sua vaga semelhança com Alan Rickman (olhe para essas bochechas e essa boca!), Acho que temos evidências suficientes para dizer conclusivamente JN - > SS . QED.

Não, ele não foi baseado em uma pessoa real.

Rowling afirma isso categoricamente em entrevista em 2004

Are any of your characters based on real people?

The only character who is deliberately based on a real person is Gilderoy Lockhart. [...] Other people have contributed the odd characteristic, such as a nose, to a character, but the only character who I sat down and thought that I would base on someone is Gilderoy Lockhart. It made up for having to endure him for two solid years.

Ele afirma o mesmo em o antigo site da JK Rowling (provavelmente escrito em 2005 ou 2006):

I have only once set out to depict somebody I have met and, unlikely though it might seem, the result was Gilderoy Lockhart.

Veja também Quem é Gilderoy Lockhart?