Werewolves have been around for many centuries. They are known as people who are inhabited by animal spirits and change uncontrollably when the spirit inhabits them. This kind of transformation would also be known as the wereman. The traditionalstory is that werewolves would change on or aound a full moon. The only thing that would be able to kill these animals would be silver bullets. Some of these animals were known to be able to change their features at will. This can be cured by supposedly excorsising the beast from the body. There are many different variations of this type of werecreature. Many different tribes have their own type of werewolf.
In Europe, a werewolf was a man who at night turns himself into a werewolf and searches for an unlucky human to devour. The werewolf had to return to his human form by daybreak by shedding his wolf skin and hiding it. If it was found and destroyed then the werewolf would die. If the werewolf was wounded then he immediately reverts back to his human self and he can be distinguished by a corresponding wound on their body.
How was this legend started? It could have easily been started by a disease known as Lycanthropy. This syndrome causes the growth of hair all over the body and the eyes become very sensitive to light. The sufferers of this disease rarely went outside during the day because of their sensitive eyes or their appearance. The first werewolf on Buffy the Vampire Slayer was in the episode "Phases" when they found out that Oz was a werewolf.