Although drawn primarily from George Waggner’s The Wolf Man (1941), which begat Lon Chaney Jr.’s career as a monster star par excellence (he would go on to play virtually every monster in the Universal catalog over the next decade), it also draws background from the oft-forgotten Werewolf of London (1936), which helped establish the on-screen lore of lycanthropy.
Curt Siodmak’s screenplay for the original 1941 The Wolfman is credited as the source for this Victorian-era retelling (there are elements also taken from the uncredited 1935 Werewolf of London) and, while great liberties are taken with the family history, it’s remains true to the basics and even begins by quoting directly from the source: “Even a man who is pure in heart and says his prayers by night, may become a wolf when the wolfbane blooms and the autumn moon is bright.”