Trivia: In Curt Siodmak's original script for the film, whether or not Lawrence Talbot really underwent a physical transformation to a werewolf or if the transformation simply occurred in his mind was left ambiguous. The Wolf Man was never to appear onscreen.
Trivia: Even though Maria Ouspenskaya plays Bela Lugosi's mother in the movie, she was only 6 years older than him.
Trivia: Lon Chaney Jr. is never referred to as "The Wolf Man" in the movie.
Trivia: The werewolf that attacks Larry is actually a dog that belonged to a security guard who worked at Universal Studios.
Trivia: Claude Rains, who in this movie played the father of Lon Chaney Jr., was in reality only seventeen years older than Lon.
Answer: Werewolves as a concept date back many years - this film originated many of the current conventions though, so the simple answer to your question is "the writers of this film". See the Wikipedia for more info - http://en.wikipedia.org/wiki/Werewolf.