Werewolves, also known as lycanthropes, are mythological or folkloric people with the ability to shapeshift into a wolf or wolflike creature, either purposely, by using magic, or after being placed under a curse. The medieval English chronicler Gervase of Tilbury associated the transformation with the appearance of the full moon; however, there is evidence that the association existed among the Ancient Greeks, appearing in the writings of Petronius, a Roman chronicler. This concept was rarely associated with the werewolf until the idea was picked up by fiction writers.
Werewolvism was an involuntary condition brought on by the full moon. At dawn, the individual would revert to human form. While a wolf, the individual retained human intelligence and memory and could refrain from bloody attack on others. If injured, the wound would heal with remarkable speed.
The condition would begin expressing itself on the onset of puberty. Dieter was such an adolescent, in early 1176 Cologne, where the transformation had begun monthly a few months previous.