There is No Historical Arthur

For there is nothing in it as it seems
 Saving the King; though some there be that hold
 The King a shadow, and the city real  Alfred, Lord Tennyson, Gareth and Lynette

Anyone who tells you otherwise is trying to sell you something.

There are certainly some elements of Arthur’s storyline which are grounded in actual historical events, and even some¹ historical figures who may have served as archetypes for the legend.

It seems unlikely, though, that there was any real person as the starting nucleus for “King Arthur” - at least not someone who remotely matches even the early legends. That is to say he’s fictional from the very first sources we get of him².

Wikipedia has more details on the debate and why the consensus takes this position now (and didn’t earlier) - and Cambrian Chronicles has an engaging video on this.

Footnotes

1. Themselves often shrouded in dubious historicity and legend. ↩

2. Which are hundreds of years after the supposed historical era Arthur is in - and records closer to the time don’t include him. ↩