But the persistent demand produced a supply; and the honour of identification with Prester John, after hovering over one head and another, settled for a long time upon that of the king of the Nestorian tribe of Kerait, famous in the histories of Jenghiz under the name of Ung or Awang Khan.
He mentions, however, a brother of this John called Unc who ruled over the Crit and Merkit (or Kerait and Mekrit, two of the great tribes of Mongolia), whose history he associates with that of Jenghiz Khan.
This Unc was in fact the prince of the Kerait, called by the Chinese Tuli, and by the Persian historians of the Mongols Toghral, on whom the Kin emperor of north China had conferred the title of "wang" or king, whence his coming to be known as Awang or Ung Khan.
But this is a mistake; for in fact the application had begun much earlier, and probably long before the name had ceased to be attached by writers on Asia to the descendants of the king of the Kerait.