Prester John, the name applied by mediæval credulity for two hundred years to the supposed Christian sovereign of a vast but ill-defined empire in central Asia. The idea of a powerful Christian potentate in the far East, at once priest and king, was universal in Europe from about the middle of the 12th to the beginning of the 14th century, when it was transferred to Ethiopia and finally found a fancied historical justification in identification with the Christian king of Abyssinia.
The first mention of a Prester John, sprung from the ancient race of the Magi of the Gospels, occurs in the Chronicle of Otto, bishop of Freisingen. Here, on the authority (1145) of the bishop of Gabala (Jibal in Syria), we find a circumstantial account of his power, his Christianity after the Nestorian pattern, his victories over the Medes and Persians, and how his progress to Jerusalem was stayed by the intervening Tigris, which refused to freeze over to give him passage. Again, about 1165, there was widely current in Europe an extravagant epistle supposed to be addressed by Prester John to the Greek emperor Manuel. Herein we read astounding wonders enough: how that he ruled over the three Indies and countless hordes of men, among them those unclean races which Alexander the Great shut up within the northern mountains; that thirteen great crosses of gold and jewels were borne before as many armies, each of 10,000 knights and 100,000 foot; that all his subjects were virtuous and happy; attendant upon him were seven kings, sixty dukes, and 365 counts, twelve archbishops, and twenty bishops, while seventy-two kings with their kingdoms were his tributaries; before his throne stood a wondrous mirror, in which he saw everything that was happening in all his vast dominions; his kingdom contained the Fountain of Youth, the Sea of Sand, the River of Stones, and the river whose sand was precious gems, ants that dug gold, fish that yielded purple, pebbles that give light and make invisible, and the salamander which lives in fire, from the incombustible covering of which were fashioned robes for the presbyter to wear. There is also extant a letter of date 1177, written by Pope Alexander III. and evidently addressed to the imaginary author of the grandiloquent epistle of 1165.
About the year 1221 the distant rumour of the conquests of Genghis Khan again gave strength to the belief in such a mighty Christian potentate. M. d'Avezac first pointed out the true historical source of the story in the Chinese Yeliu Tashi, founder of the empire of Kará-Khitái, who assumed the title of Gur Khán (supposed by Oppert to have been confounded with Yukhanan or Johannes), and fixed his capital at Balasaghun, north of the Tian Shan range. He defeated Sanjar the Seljuk sovereign of Persia in 1141 at a great battle near Samarkand, but, though hateful to the Moslem historians, of course never made any profession of Christian faith. Professor Bruun of Odessa identifies Prester John with the 12th-century Georgian prince John Orbelian, a redoubtable enemy of the Turks (see Colonel Yule's Marco Polo, 2d ed. 1875, app. to vol. ii.). Many writers about the close of the 13th century, as Marco Polo, the Sieur de Joinville, and even Gregory Abulfaraj, identify him with Ung Khán, king of the Nestorian tribe of Kerait. Friar Odoric about 1326 visited the country—the Tenduc of Marco Polo—still ruled over by a prince whom he styles Prester John, but he adds, with the cautious gravity of the true historian, 'as regards him, not one hundredth part is true that is told of him as if it were undeniable.' From this time the Asiatic phantom entirely disappears from view, but from the 14th century onwards Prester John continues a less romantic existence under the guise of the Christian king of Abyssinia.
See D'Avezac in vol. iv. (1839) of the Recueil de Voyages et de Mémoires of the Paris Société de Géographie; Dr Gustav Oppert, Der Presbyter Johannes in Sage und Geschichte (2d ed. 1870); Friedrich Zarncke, Der Priester Johannes (1876-79). See also Colonel Sir Henry Yule's article in Ency. Brit. (9th ed.), his Hakluyt Society Cathay and the Way Thither (vol. i. 1866), and The Book of Ser Marco Polo (2d ed. 1875).