Herbert Marshall had the lead role of agent Ken Thurston/"Mr. X" who took on dangerous cases in a variety of exotic locations. Leon Belasco played Mr. X's comedic sidekick, Pegon Zellschmidt, who always turned up in remote parts of the world because he had a "cousin" there. Pegon would annoy and help Mr. X. Wendell Niles was the announcer from 1947 to 1948. Gordon Jenkins Orchestra supplied the background music. The series was created by Jay Richard Kennedy who later adapted The Man Called X as a 39 episode syndicated television series (1956-57) starring Barry Sullivan as Thurston for Ziv Television.