"And I'm not a very popular dinner guest with most of the community. It's an occupational hazard of being a werewolf."
-- Remus Lupin (OP5)
A werewolf is a human who has been infected with lycanthropy.
The werewolf is a most unusual creature in that it doesn't technically exist except for a brief period of time around the full moon. At any other time, a werewolf is a completely normal human. However, the term werewolf is used for both the wolf-like creature and the normal human. Remus Lupin is a werewolf by definition even if he isn't in the actual form of the wolf.
A werewolf comes into being when a person is bitten by another werewolf. Once this happens, the person must learn to manage the condition. Modern potion-making has come up with a draught called Wolfsbane Potion which controls some of the worst effects of the condition (PA18). Wolfsbane Potion is quite difficult to make, even for fully qualified wizards, and is said to have a rather disgusting taste (PA8). Nothing will completely cure a werewolf, unfortunately.
A werewolf when transformed is a fearsome beast indeed. All trace of human awareness is gone and the werewolf will attack any witch or wizard, including the werewolf's best friends. This transformation is triggered when the moon is full, although there is some evidence that a werewolf who is taking a regular regimen of Wolfsbane Potion will not transform until the moonlight actually strikes him. (Lupin, for example, did not transform while he was in the Shrieking Shack, even though the moon was full, until he stepped outside and the full moon emerged from behind a cloud. Lupin had been taking Wolfsbane Potion for months.)
Bill Weasley was bitten and slashed by a werewolf, Fenrir Greyback, in the Battle of the Tower. His face was severely damaged with magical wounds which might not heal properly. Because the werewolf was not transformed into a wolf, he will likely not become a werewolf himself.
- Discussed in Defense Against the Dark Arts class (PS13, CS10), with an essay assigned by Snape when he once substituted for Lupin, although werewolves weren't due to be covered until the last chapter of the third-year DADA textbook (PA9).
- Werewolves have been mentioned several times in connection with Harry's Defense Against the Dark Arts teachers. Quirrell had encountered them in Black Forest (PS5), and at one point discussed in class how to treat werewolf bites (PS). Gilderoy Lockhart, supposedly, once defeated the Wagga Wagga Werewolf (CS10), something that may be discussed in his book Wandering with Werewolves (CS4). Lockhart eventually confessed to Ron and Harry that an 'ugly old Armenian warlock' had actually performed the rescue of a village from werewolves that he himself had taken credit for (CS16). Remus Lupin, of course, is a werewolf (PA18, OP5, OP28).
- Draco Malfoy as a first-year had heard that werewolves lived in the Forbidden Forest (PS15), and a year later Ron Weasley referred to the same rumor (CS15). The fascinating origin of this rumor can be found on the "werewolves" page on Pottermore. (Pm)
- Tom Riddle alleged that Hagrid raised "werewolf cubs" under his bed as a youngster (CS17). (This, according to JKR, was a slanderous lie from Tom Riddle, since werewolves don't have "cubs".)
- The Ministry regulates werewolves. Already in 1637 there was a Werewolf Code of Conduct (PS16). Dolores Umbridge was instrumental in the passage of restrictive anti-werewolf legislation that Sirius said made it almost impossible for Lupin to get a job. (OP14)
- According to Newt Scamander, werewolves have been shunted between the Beast and Being Divisions of the Department for the Regulation and Control of Magical Creatures for years. At one point, the Werewolf Registry and Werewolf Capture Unit were both in the Beast Division, while at the same time the office for Werewolf Support Services was in the Being Division (FB).
Werewolf comes from the Old English wer, meaning man, so it literally means man-wolf.
Werewolves have been dredged up and down paranormal fiction, especially in more recent years. Usually, werewolves are considered creatures of evil.
Rowling mentioned in interviews and on Pottermore that werewolves are supposed to be a wizarding world comparison to HIV and other blood-borne illnesses, and peoples reactions to them.
"Professor Lupin, who appears in the third book, is one of my favourite characters. He's a damaged person, literally and metaphorically. I think it's important for children to know that adults, too, have their problems, that they struggle. His being a werewolf is a metaphor for people's reactions to illness and disability."
-- J.K. Rowling (Scot)