In 1220 CE, St. Francis of Assisi tamed a ferocious werewolf terrorizing Gubbio, Italy—transforming "Brother Wolf" from savage beast to peaceful townsperson. But why did Christianity need to conquer the wolf? For millennia, werewolves have stalked the boundaries between civilization and savagery, humanity and monstrosity. From ancient Mesopotamian curses to Greek myths of divine punishment, from medieval theology to early modern courtrooms where hundreds died in werewolf trials, the shape-shifter has embodied our deepest anxieties about human nature itself.