Prester John

Prestor John was a legendary priest-king during the middle-ages, and believed to be the keeper of the Holy Grail.

Henry Jones mentioned him and his connection to the Grail legend in his Grail Diary

Behind the scenes
Prester John was a legendary figure of an obviously non-existent king in an unknown country of the Far East. He was believed to be a descendant of one of the Three Magi.

Prestor John is not mentioned in the dialogue, however a picture of him can be seen in the Zeppelin scene.

Appearances

 * Indiana Jones and the Last Crusade