As Marie de France tells us, a werewolf as traditionally understood is "a savage beast when the fury's on it" - and, if we follow the reading where his wife's powerful fear of angering him is a telling one, her werewolf meets this description as much in his untransformed state as in his transformed one. But part of the point of the folktales typed as AT449 (which includes both Marie's "Bisclavret" and the Arthurian tale of Melion, which it greatly resembles) is the fact that they present the werewolf as victim rather than as monster, whereas Marie's prologue makes it clear this is an unexpected reversal.
What did a medieval audience expect from a werewolf tale?
For starters, they didn't - such stories were rare, and surprising; that's probably part of why Marie feels the need to start by explaining some things about what a werewolf even is. There were some stories in Germanic lore, though they seemed to have been suppressed with the coming of Christianity.
But by the late medieval and early modern periods, belief in lycanthropy was on the rise. And to the early modern people who told of such things, they were not merely a subject of horror fiction, but a real danger in the world. French court records show that from 1520 to 1630, approximately 30,000 people were convicted of being werewolves; most of these were then burned at the stake. Most of these people were believed to have committed at least one murder while in wolf form; many even confessed to such. France was far from alone; Germany had its fair share of werewolf trials as well, and more are recorded in the rest of the continent.
The story of Gilles Garnier, the werewolf of Dole, is a fairly typical example of the substance of the stories these records tell. Garnier was a recluse who lived outside the town of Dole, in eastern France, with his wife. According to his confessions, he was witness to a spectral apparition in October of 1572 which left behind an ointment Garnier could rub on himself to become a wolf. This he did, and then, in the form of a wolf, stalked and murdered a ten-year-old girl, eating some of her flesh on the spot and taking the remainder home to cook for himself and his wife. Within a span of two months he accumulated a total of four alleged victims, all preteens; of the four, two attacks were interrupted by witnesses who drove the wolf away before the children later died of their injuries. It's clear these two were, in fact, the victims of an animal attack.
Garnier was found wandering in the woods in December, his hair long and matted, his face bloodied, with the body of a child in his hands. He was arrested, tried for witchcraft and lycanthropy, and burned at the stake in January of the following year.
The precise means by which werewolves assume their lupine form in these documents vary. An ointment is the most typical, and it's usually a gift from a man (physical or not) who dresses all in black and is sometimes implied to be the Devil. Others claim to turn their skin inside-out (revealing that it is hairy on the inside), to don an enchanted wolf pelt, or simply to be the victims of some wicked sorcery which causes them to become a wolf against their will from time to time. A few even seem to have carried out their attacks by a sort of astral projection, wherein their soul takes on the physical form of a wolf and hunts while their body lies asleep. Many of those convicted seem, in the modern day, to have been victims of some form of mental illness; in some cases the evidence that they were serial killers is reasonable (in fact in at least one "werewolf" trial there is no record of any actual transformation), while others may have been utterly innocent of any violent crime whatsoever. Nearly all suffered the same fate, however - burning at the stake, which was in those days the standard punishment for lycanthropy.
This was not, it should be noted, a result of the Inquisition. In fact, Catholic authorities generally condemned the werewolf trials (though some endorsed the concurrent witch-trial craze), and the Inquisition did not take part in the judgment of "superstition." Perhaps, given this more grounded view of the matter, things might have gone better for society if the Inquisition had taken a hand in these cases; it's entirely possible they would have concluded that they were trying murderers, or recognized that some of the accused were ill. By the end of the sixteenth century, such a transformation begins to be seen in the conclusions of just some of the secular judges; Jacques Rollet was sentenced to a madhouse rather than to death in 1598, and in 1603 a developmentally disabled boy who confessed to charges of lycanthropy was released when the judge found that his transformations existed only in his mind, and thus was not something for which he could be rightly punished. Over the course of the following decades, the conviction rate for lycanthropy cases dropped off, and charges were brought with greatly reduced frequency. But the idea remained, and for a time people continued to fear that if they ventured into the woods at night, they might be set upon and devoured by a wicked man in the form of a wolf.