In modern culture, we often imagine a King having atleast one wizard or magical user giving mystical advice, the most famous being Merlin. Was there any truth to this? Obviously not talking about actual wizards, frauds or "mystics" without demonstrable powers count just as well.
Follow-up: How much does this trope have to do with Elizabeth I's association with John Dee? I know they're Early Modern rather than Medieval, but it seems to me that they had the closest thing in Western Europe to an Arthur-Merlin-type relationship.
What would you count as a "wizard"? This is right before your suggested period, but would someone like Kardīr, the Moabad (High magu, i.e. Zoroastrian cleric, related to "magic") who served as an adviser to several Sasanian Great Kings count? I could probably go on a bit about that this evening (in 12h) or tomorrow.
Needless to say it would be highly unusual for a monarch to hire a "wizard" to perform "magic" if the magic was not a sanctioned part of the dominant belief system, so I'm not sure what else you might have in mind...