Mari, or Mari of Anboto, is the quintessential "sorgina" in the Basque folklore. Sometimes is refered as a godess that inhabits all mountains, instead of a witch.
How much of that is due to popularisation over the last 150 year and how much is actually backed by traditional folklore?
for the slavic people I'd say Baba Yaga, but the earliest records of her tale are from the 18th century. Not sure how far back the tale actually started.
Much longer than 150 years, but very little actual folklore.
Merlin as we know him is a 12th century literary creation. Largely an amalgation of 2-3 different semi-historical/semi-legendary personages who individually were far less known than Merlin came to be.
Lots of the well-known elements of the Arthurian Mythos got added during the 12th century, and got its close-to-final form during the early 13th century.
That gives the source of the mythos, but when did the popularity rise to the exclusion of other stories? Did Merlin dominate national tales in the 12th and 13th centuries? Or was he just one out of many wizards living in concurrent stories until modern pop culture?
The whole Arthur cycle was very popular during the late 12th and early 13th centuries.
It was the Game of Thrones of that era if you wish. Except of course that elements of the Arhurian Mythos was believed to be true back then.
I hadn't quite anticipated that.
Still, a British character that gets to hear the better bard/troubadour/travelling storytellers often enough that they have a passing familiarity with what we now call the Matter of Britain, would likely know the name Merlin, and think he was the most famous magician.
Actually, browsing Wikipedia suggests Merlin (and King Arthur) is quite well known in Brittany as well.
I don't have an english labguage link on hand from it, but medieval jousts would sometimes be massive Arthurian LARPs where the various contenders would take on the persona of famous Arthurians knights. In France Chretien de Troyes popularised the Arthurian topic (and remained in the school curricula at least until the 1990s).
According to this text :
A la fin du XIIIe siecle, la legende Arthurienne est tres en vogue en Picardie, Flandre et Hainaut.
At the end of the 13th century, the Arthurian myth is trending in Picardie, Flanders and Hainault.
I'm slightly struggling with the notion of "national" wizards, which smacks a bit of the modern nationalist ideal of culture and belief conveniently mirroring modern political divisions. But moving past that...
It is intriguing to speculate to what extent the "pre Christian" notion of gods-as-ancestors survived into the 13th C in popular thought. What has come down to us is the opinion of the educated elite, who did their best to reconstruct pre-Christian belief in light of Christian theology and what they knew of classical literature (thinking especially of the suspiciously neat view of the Norse gods as a remarkably well organised pseudo-Roman pantheon with Christian overtones). Earlier beliefs may well have seen the "gods" as much more human, and as supernaturally accessible ancestor figures/forces. If these stories survived into the 13th C, then many of the figures we see as "gods" may well have been considered legendary sorcerers.
But I suspect that is far fetched.
Yet my suspicion is that there would be few over-arching "great" wizards revered on a "national" basis. Instead, local traditions would tell tales of individual characters relevant to the specific locale. Families and regions will have their stories, within which there will be sorcerers - a family in Sweden may be listening to the story of the sorcerer Kolr in the saga of Thorstein Vikingr's Son, because they see it as part of their family heritage, while a family a few hundred miles away would have no interest in the story and so not think of Kolr; today we might assume that everyone in Wales would know the story of Gwydion fab Don, but that's only because the Mabinogion happened to be preserved and came to be touted as archetypically "Welsh" by later romantics and scholars - quite possibly he would only have been known very locally.
We can't know... but I suspect we should be suspicious of assuming that homogeneous stories would be so broadly ubiquitous in the 13th C as in, say, the 19th, 20th or 21st centuries.
I really like your thinking here.
But I also am not sure we moderns fully understand how oral traditions were working in that era and how they impacted some of that thinking of the magic/mystical/divine as more human.
Traditional literacy was very limited and highly controlled in the 13th Century. I suspect storytelling and stories followed trade routes and patterns of language migration as much as they followed national boundaries as traders and other travelers passed stories on from village to village like a sort of news and entertainment service.
I have a vague recollection from my grad school days, that when Asbjørnsen and Moe collected and published the folk tales that they had gathered during their travels in the fjords and mountain villages of western and southern Norway, that they found a lot of common stories structures with local variants and flavors that could almost be traced from village to village by the ease of travel or trade between them. I could be totally wrong.
But to your point, writers and scholars like Asbjørnsen and Moe were re-creating these tales into a national identify at the same time as they were preserving them as a national legacy. It's super hard to disconnect that complex web, but clearly these fantastical tales stuck around these towns and villages as isolated as many o them were.
I still imagine that oral traditions were far stronger at preserving stories than we might imagine from our 21st century point of view where we have so little reason to remember or memorize anything because of the ease with which we can find or record information on the technology in our pockets.
Even in my short 50+ years, I've moved from a time when I had countless phone numbers memorized to a point now where I only don't even have my own children's cell numbers memorized.
I suspect we've lost a lot of the art and science that kept oral traditions alive for centuries.