King Arthur has proven to be at his best as an entertainer, by proxy at least. :^)
My favorite of the “real guy” genre is this:
https://www.thriftbooks.com/w/king-arthur-the-true-story_graham-phillips_martin-keatman/422768/
Boorman also thought Merlin the most interesting character. Someone who's fatal flaw was that he didn't understand human love or emotion. That's why Morgana so easily tricked the brilliant Merlin. Merlin knew much, but had no knowledge or experience with love. With Morgana, Merlin was like a virgin schoolboy in love for the first time.
The studio compelled Boorman to change the title to Excalibur.
One of my favorite movies when I was a youngster. First video tape I ever asked my parents for. Wore that sucker out till it got et by the VCR.