[Charles Martel]

The current theory is that this is a very old European prejudice dating to when most folks sporting ginger locks were Neanderthals, since the Neanderthal genome seems to code for red hair.

Seems like the historical prejudices against the Scots and Irish might have more to do with it. At least in parts of the U.K.

[The_Reader_David]

But that theory doesn’t account for the same prejudice in Greece, nor for the Western-Europe-wide association of red hair with witchcraft and vampirism in the Middle Ages.