I never pretended to have written anything more than pure speculation, Ursuul.
As for other kings, Oberon seems to be implied to have been one, but it's kinda unclear. From this Reddit AMA: reddit.com/r/Fantasy/comments/13iexg/hi_im_jim_butcher_im_the_guy_who_takes_credit_for/?utm_source=amp&utm_medium=comment_list
Q: 5. You've described Santa Claus as being the Winter King. What does that title mean? Do Winter and Summer each have a trinity of Father/King/Prince, like they do with Mother/Queen/Lady? Is the King necessarily the consort of the Queen? If so, will we be seeing Oberon at some point?
A: 5) The Faerie realms just aren't that structured. It's more accurate to say that he is /a/ Winter King. Or even more accurately, that he is a free Wyld Fae who is of a power level that is on par with Mab's and happens to neighbor her sphere of influence, and finds it simpler to show up to family dinners during the holidays and make polite than to start staking out boundaries and establishing treaties.
Oberon... well, the guy kind of wound up between Mab and Titania in one of those romantic triangle things, back around Shakespeare's day. He didn't make it.
The question and the answer unfortunately does not make it clear what court Oberon was a king of, or even if he was a king at all. But he is a possibility.
Maybe it's a cyclical thing? One of the pseudo Kings become a temporary King proper over the others, set at specific periods of the year. That brings to mind that it could be something similar to the Wiccan Wheel of the Year, with dates having to do with equinoxes and solstices being significant.
Like, Kringle could become Winter King on the Winter solstice, hence why he is the most known (and powerful?), while Erlking becomes Summer King on Halloween maybe.
It's not a contradiction. Anon should have watched the video, because Jim explains what he means:
"Where are the Farie kings? Do they exist?
Yes they do. The Erlking as sort of the Hunter king, and Santa Clause, the Winter king who is not the commercial Santa Clause. The kings are sort of the opposite of the queens in their given season. They are independent of their Queen’s courts. The Erlking is a summer king and he is not a particularly friendly guy, whereas Santa Clause, one of the winter kings, is kinder, the spirit of generosity in a time of bleakness. Yah I’ve gota have Harry ask Mab about him so she can roll her eyes."
The Erlking is a Summer King, not the. He is also independant of the Summer Court so it's not like he is the consort of the Summer Queen or anything.
Nah, Word of Jim:
Q: Is the original Merlin still alive?
A: Kind of… life… death… it’s kind of a squishy line in the Dresdenverse.
Doesn’t sound like “prisonner on an island.”
Besides that, the original Merlin is older than the modern British accent. I would actually expect him to speak ye olde Englishe. Though I admit this one is a poor point since He Who Walks Behind and Nicodemus both have British accents as well.