Insane scientists are often seen in horror movies and science fiction. But those characters were just copying the mad scientists who actually existed in real life. Some of these scientists shaped history, but they were totally mad!
Johann Conrad Dippel
This German physician was into alchemy and theology, stealing and doing experiments on cadavers. He also searched for the Philosopher's stone and tried to create artificial intelligence. He did create "Dippel's Oil", an insect repellent that was used in WWII. He was born in Castle Frankenstein. This connection leads many to speculate that Dippel was the inspiration for the Frankenstein novel.