King Arthur is a bit of a stretch. Though there is evidence in Normandy, Brittany and southern England of architecture or peoples who were inspiried by an Arthur-figure, there's very little historical evidence that such an individual actually existed. In my studies, he is an almagamation of French and English noble ideals and a tidy way to bring pre-Christian values/holidays/myths into the increasingly prevalent Christiandom of Europe.
I think Arthur safely falls into the disputed category given here. Most of the stories we have now are clearly fictional, but there are enough references from the few surviving records of writers relatively near the time to suggest there at least might have been an actual British military leader that the legends were later applied to.
I should've paid closer attention to that "existence is disputed" note. I think it's appropriate to keep them all because usually someone what that name did exist, even if they didn't do everything its said they did or multiple people did it. But if you wanted to bold the existence note, for the careless like myself I'm sure someone will appreciate it. Nominated.
Very surprised Alfred the Great was on here and not William the Conqueror. Very good and challenging quiz. Although some of these questionable “fairytale” ones such as Ragnar and Arthur shouldn’t be included