Otto of Freising was eager to ask him to reattempt an endeavor frustrated by the flooding of the Tigris, namely an excursion from his capital at Ecbatana in Persia to capture Jerusalem.
Joao II sent an envoy to this ruler, possibly encouraged by a report of a prior letter received by Byzantine Emperor Manuel I Comnenus. Otto of Freising was eager to ask him to reattempt an endeavor frustrated by the flooding of the Tigris, namely an excursion from his capital at Ecbatana in Persia to capture Jerusalem. This "king of the Three Indies"  had an army of 140,000 cavalry and 100,000 infantry, and his grandson David's conquests in Persia and Iraq encouraged the Bishop of Acre until it was discovered that this was actually the work of Genghis Khan. The Ethiopians were just as confused when the Christian states of Europe insisted that this man was their Emperor. For 10 points, name this mythical Nestorian Christian priest-king who supposedly ruled an isolated and wealthy kingdom east of the Muslim lands.
Joao II sent an envoy to this ruler, possibly encouraged by a report of a prior letter received by Byzantine Emperor Manuel I Comnenus.
{Prester John} [or {Presbyter Johannes}]