The Mongol empire was founded at the end of the twelfth century by Genghis Khan. He ﬁrst allied himself with the Christian prince of the Keraits, Togoril, who did not lead a particularly Christian life but who very probably became the original model for the priestking John. Togoril ﬁrst had to prove himself against his uncle GurKhan; with help from the Kin people of Peking he defeated the Tartars and as a reward received the title “Wang-Khan” or “OngKhan” from the Chinese court; with this title, he entered history. Genghis Khan’s father, Jesügei, also helped Togoril achieve victory over his uncle. However, disagreement later developed between Genghis Khan and Togoril, and Togoril was murdered in 1203 while trying to escape. Over several generations, the family of the great Mongol khan intermarried with the family of the “Gurkhans.” From the Persian historians Juvaini and Raschid ad-Din, we have precise information about these genealogical connections. Genghis Khan wed Togoril’s daughter Ibaqa-Beki, his eldest son Jochi her sister Bek-Tumish, and his son Tolui († 1231) her sister Sorqaqtani-Beki. The latter became mother of the great khans Mongke and Kublai, as well as the Il-Khan Hulagu, who were fond of the Church of the East because of their mother, though they did not themselves convert to christendom.