На чем основана история:
CHRIS CHIBNALL: We have a grand plan, which if we get things right, I hope will allow for multiple seasons. We are telling the story of Camelot, using Thomas Malory’s Le Morte d’ Arthur as our source and base material.

Файнс о своем персонаже:
FIENNES: I think what I’ve gone for is more of a warrior-monk, and less of the zen Obi-Wan that he might get to eventually. At this moment, he’s far more hands-on. He’s visceral. He can take care of himself. He probably won’t always draw on his powers.
It’s more wit and intelligence and the political that Merlin relies on rather than magicking him into power because that would be deceitful.
I think of Merlin as a cross between Obi-Wan Kenobi and Donald Rumsfeld, in that there’s this very strong political agenda.
Yes, there will be some dark arts, and we’ll see people changing shape and things disappearing, but over and above all of that, the real potent magic is the birth of the legend.

Об отношениях Мерлина и Артура:
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За пост спасибо  дядя Митя, источник информации и полный текст интервью тут.