Prestor John? Lol.
During Ghengis run against Islam the west heard of a Christan king in the east laying waste to the islamic world. They were so happy, figuring they now had the islamic world caught in a great pincer movement.
Of course there was no Prestor John, just Ghengis, who almost nipped islam in the bud.
But Ghengis believed in as much celestial insurance as possible, therefore you were allowed to pray to the gods of your fathers, so long as you prayed for the well being of the Khan.
Prestor John was actually believed to be an African king in Abysinnia. The belief in Prestor John’s Christian utopia predates Genghis and the crusades.