Werewolves are a longstanding feature of European folklore, with references to men who can turn into wolves dating back to at least the Ancient Greeks, although the belief does not seem to have become widespread before the Middle Ages. For most of this time, however, werewolves seem to have been thought of as evil sorcerers or (in pre-Christian times) one-off individuals cursed by the gods. This "evil sorcerer" version most closely matches the sort of werewolf seen in the works of Tolkien and C.S. Lewis and is quite different from the D&D version.
That instead borrows from horror fiction, most notably the Universal Pictures Wolf Man films of the 1940s. Many of the tropes we associate with werewolves today were made popular by those films, and, in fact, often don't date back much further than the 19th century. In these films, however, as in some more modern examples such as An American Werewolf in London and Harry Potter, werewolves are portrayed as (mostly) tragic individuals, while in Twilight they seem relatively benign. D&D, like many other RPGs, makes them definitively evil although the potential for tragedy is still implicit in their ability to pass on the condition to others.
