Egyptian mythology

In 1990, Werewolf researcher Hugh H. Trotti (Beasts and Battles: Fact in Legend and History) offered a highly original explanation of the Werewolf myth.  He noted that the ancient Egyptian cult of Anubis, whose priests wore a wolf-like mask representing this jackal-headed god of death, eventually became established in Rome where Anubis became known as Hermanubis. More precisely, he is the fusion (mashup) of Egyptian Anubis and Greek Hermes.

By the 1st century AD, moreover, many statues of jackal-headed humans representing Hermanubis had been erected there.

Accordingly, as suggested by Trotti, Germanic troops recruited into the Roman armies who saw priests of Hermanubis wearing their lupine masks, and who also observed the jackal-headed statues would certainly have remembered and referred to them long after the fall of the Roman empire. 

In turn, it would not be difficult for distorted accounts of these priests and statues to give rise in time to stories of men who could transform into wolves.

But conversely, it could be the Germans who brought to Rome their adoration for the wolf and manage to revive it through the evocation of the old Egyptian God.