Beginning in the summer of 1944, at the height of World War II, The Man Called X was originally a kind of "FBI" program. The series soon developed a more international approach, however, featuring danger, intrigue, and romance in exotic settings. On any given Saturday or Sunday evening, Wendell Niles would say, "Wherever there is mystery, intrigue, romance, in all the strange and mysterious places of the world, there you will find "The Man Called X".

The Man Called X starred British-born actor, Herbert Marshall as suave, sophisticated Ken Thurston, undercover international troubleshooter for a mysterious American governmental agency. He is aided and abetted by that shady character Pegon Zeldschmidt played by Leon Belasco. The Man Called X was underwritten by various companies, most notably Frigidaire and General Motors as dual sponsors. The show was directed by Jack Johnstone, and Johnny Green is credited with its music.