Need a non theological answer than quoting a holy book which says Satan chose the beast.
Start with what /u/AncientHistory wrote about Where does modern Satanic imagery come from?
Also /u/sunagainstgold has previously written about how well French peasants understood religion because European life in the Middle Ages is hard to separate from religion and implicit/explicit theological claims. See also "But who prays for Satan? Who in eighteen centuries, has had the common humanity to pray for the one sinner that needed it most?"