Ruler of the Mountains can be found in the Tort Region of Sand Land, in the Pterano Nest northwest of Spino. There is a Water Resupply Point slightly north of the nest that will get you very close.

So let's say you've experienced all that Crusader Kings 2's vanilla has to offer (you haven't), you've played all of the big and well-made mods out there (you haven't) and decide you've earned ...