Werewolves
While most think of Werewolves from old black and white movies of the past or even newer books/movies like Twilight, the idea of werewolves has existed for hundreds of years. The usual story is that someone is cursed by some type of magical being or bitten/scratched by a werewolf. The person will then transform into an uncontrollable half wolf/half man during a full moon. This European folktale was first referenced by Roman courtier Gaius Petronius Arbiter, who wrote about them sometime between 27 to 66 CE. Gervase of Tilbury, a canon lawyer, was also important to their development. He referenced them sometime between 1150 to 1228 CE.
Due to the heavy connection to medieval folklore, werewolves were thought to be real. Christians then began to connect them to the occult and would hunt believed werewolves down. They’d execute suspected werewolves the same as they did those suspected of using witchcraft. While they were mysterious animals or creatures thought to be a myth, werewolves were kind of real. Essentially, a person would be bitten by some sort of canine, such as a wolf. They would then develop a fatal illness that made them crazy. It is quite likely they were infected with rabies, which can make people go nuts until their death.