Who would, say, the English use as their political boogeyman in the first half of the 20th c.? What about citizens of medieval kingdoms?
This question gets asked a lot. You might check out the FAQ section I've linked below while waiting for other answers. TLDR is, it depends, but in the Christian West, Judas Iscariot and Atilla the Hun are probably most common, although lots of individual places have their own boogey-men.