According to legend, werewolves are born human, but become werewolves after being bitten by one or infected by one’s blood. A werewolf appears human most of the time, but turns into a wolf-like creature typically at the full moon -- usually described as the three nights around the apex of the full moon. A werewolf has no sanity whence transformed, and will not stop at prey. Werewolves will harm anyone they see, except other werewolves, of course. The werewolf is said to look like a normal man or woman when there isn't a full moon but they can transform into their werewolf form at the full moon.
Descriptions of werewolves' wolf forms vary. Some describe them as anthropomorphic wolves. Some describe them as four-legged wolves, sometimes larger than regular wolves, sometimes not.
- Wolfsbane (also known as monkshood) or mistletoe will repulse a werewolf. If werewolves drink substances containing wolfsbane or mistletoe they become unable to transform, although they will appear sickly.
- A werewolf can be killed by silver weapons, such as the classic silver bullet. A silver stake to the heart can kill a werewolf. However, this usually applies to "undead" creatures, and the silver weakness was decided by films.
- Wikipedia's article on werewolf