It’s a plug for a new series of novels, but I appreciate the way in which the (very brief) introduction to Prester John was done here. [Using Spider-Man to explore Christology made me smile too].
See Medieval mysticism explained with lolcats and action figures.
I’m trying to think back to any other recent fiction that picks up Prester John in some form. The only one I can think of off the top of my head is Tad Williams’ Memory, Sorrow, and Thorn series of books with King John Presbyter in them.