Trying to Find a Horror Trope

I'm writing a horror themed d&d adventure (yes I've heard of Call of Cthulhu) and I've created an antagonist who seeks to learn about death by watching others die. Eventually they get the idea that the longer it takes people to die the better they're able to learn about death, which of course leads to long draw-out torture.

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After I wrote this down I realized that it sounds very familiar, but I can't think where I might have heard of a character doing this. Can anyone think of one? I apologize if there's an obvious answer that I just don't know, there are many gaps in my horror knowledge.