Both King Arthur and the historical figure and genocidal a-hole Boudicca has, ironically, been co-opted into the supporting myths of the post-Conquest monarchy of Great Britain.
It's not unlike the mythical Scottish resistance to Roman rule (it never happened) and the ridiculous "battle that stopped Rome" cooked up about the miserable failure, flash-in-the-pan turncoat Arminius, adopted as if he was ancestral to modern Germany, which instead is descended from migrants who replaced those people from whom Arminius sprang.
😅 Well, there is Hadrian's Wall.
***the ridiculous "battle that stopped Rome" cooked up about the miserable failure, flash-in-the-pan turncoat Arminius***
This Arminius?
With that winged helmet he looks a bit like Mercury/Hermes. (I'll fly away, oh glory...)
A serious concern of JRR Tolkien.