Yes, people very much believed that some men could take or were compelled to take the form of a wolf. Here is an excerpt from my Introduction to Folklore, which may help; feel free to ask questions:

The nightmare and the werewolf are two creatures that deal with the human spirit in a way different from other beliefs related to the soul. People believed that these were the products of bizarre transformations endured by innocent people who are unaware of the circumstance. While the nightmare was a traveling spirit of a woman, the curse of the werewolf affected men. In both cases, European peasants regarded them as victims of witchcraft. The cause of their suffering was that their mothers had used magical means to avoid the pains of childbirth, leaving their children to suffer these unnatural afflictions.

In the case of the nightmare, while a woman “went mare,” as it was called, she traveled the land to plague others. She frequently appeared as a mouse that would sit upon the chests of men, giving them horrible dreams.

There are many legends dealing with this motif. One tells of a young man who repeatedly suffers from a nightmare. His mother searched the house and found an opening large enough for a mouse. That night, when her son was in the throes of a nightmare, she plugged the hole and put a pot over the boy’s chest. The next morning, she removed the pot. A mouse jumped off the boy and transformed into a beautiful young woman. That very day, a woman in a nearby village died before waking.

Some variants of this elaborate story – Migratory Legend 4010, “Married to the Nightmare” – go on to tell how the young man married this strange visitor. They lived a happy life until one day the woman and her mother-in-law quarreled and the old woman told her daughter-in-law how she arrived in the household. She then removed the plug from the wall, and the young woman changed into a mouse and disappeared forever.

This echoes a motif usually found in folktales – which are sometimes told as legends – involving the magical bride captured because her garment of swan wings or seal skin is taken and hidden by the hero. One day, the woman finds her hidden magical wings or skin, and she is compelled to return to her former shape and life. This was an ancient story that combined with the idea of the nightmare.

The werewolf was the male counterpart of the nightmare. While this cursed man sleeps, his spirit travels the land in the shape of a wolf. Unlike the nightmare, who merely gave bad dreams, the werewolf kills livestock and people, having a particular affinity for pregnant women. Like the nightmare, the man sleeps unaware that his soul prowls the land in animal form. His identity is discovered when he is wounded in wolf form or someone calls out his name. Werewolf stories can conclude with the disenchantment of the man, but some also end with his death.

The idea of the werewolf draws on a much older belief in shape shifting. There is clear evidence of a widespread European tradition that people, and men in particular, intentionally took animal forms through magical means or special talent. This belief appears in the Satyricon, the first-century Roman work of Petronius, described above. In this story, a soldier who is a versipellis, a skin-changer or werewolf, is walking among some tombstones one night when he removes his clothes and urinates around them. The clothes turn to stone, and the soldier becomes a wolf. That night a wolf kills some sheep, but a slave tending the animals pierces the wolf in the neck. The next day, the soldier, in human form, is found to have a wound in his neck.

Christiansen classifies stories of this kind as Migratory Legend 4005, “the Werewolf Husband,” in which a man’s wife discovers that her husband is a werewolf as indicated by wounds that he has received. The act of recognition releases the man from the spell. Ella Odstedt in her Varulven i Svensk Folktradition (1943) describes three principal ways in which a man becomes a wolf: the man’s mother had magically avoided pain in childbirth, and this brought a curse on her child; a curse is magically placed on a man by another person; or the werewolf actively and magically brings about his own transformation. Odstedt suggests that the last of these causes is the oldest. Dag Strömbäck supports this suggestion. He further points out in his Folklore och Filologi (1970) that Old Norse sources confirm the idea that men magically caused their own change.

There is evidence that Marie de France, a twelfth-century author from the nobility, helped spread the idea of the cursed werewolf who cannot control his own magical change. She wrote a widely-distributed story containing this motif. Because of the power of the written word in folk tradition, Marie de France may have had a role in changing the story as popularly told, making the werewolf the victim of magic as her version ascended in importance over the older tradition of a man intentionally changing himself.