Manuel I Komnenos
Brooks (p. 18) cites Karl Helleiner (p. 56), who posits:
I believe Prester John's letter was written, in part, as a piece of anti-Byzantine
propaganda, perhaps by a man who served the political interests of the Norman
princes of Sicily, or by a German... who resented the monopolistic claims of the Greeks to the Imperial
dignity, claims, be it remembered, that were very stoutly maintained by Manuel Comnenus.