Don Alfonso wrote:
How many of them appointed regents in the High Middle Era?
No idea. What did medieval nobles who went on crusade? (the only example crossing my mind ist Richard Lionheart and Prince John (and Robin Hood...)
My understanding is that most cases where a regent was appointed was if the rightful heir to the throne was still a child, someone would rule in his place till the child became old enough to rule. Often this would be the task of the former king's brother.
I think Richard Lionheart's case of a King leaving his kingdom for such a long period was very rare in the real world, but perhaps more common in settings where adventurers become rulers. Most nobles who joined the crusades were younger brothers and landless nobles who wanted to get their own dominions in the Holy Lands.