Contrary to the title of this episode, the man called "X" is not Vladimir Putin. Instead he is Ken Thurston, a global troubleshooter played by Herbert Marshall. When I say global, I mean it -- as far as I can tell, episodes of this show took place in at least 190 locations, from Thurston's own back yard to the most exotic of countries.
The Man Called X began in 1944 as a summer replacement for CBS's Lux Radio Theater with eight episodes. In the beginning Thurston was a private detective, but before the first season was over the show had edged toward espionage themes. It's success as an espionage series followed that of other popular radio shows such as Bulldog Drummond and Counterspy.
The show's second season started shortly thereafter (in September 1944) and marked a move to the NBC Blue network. The first four seasons of The Man Called X have been lost to time, but we now the espionage theme (usually bad Nazis) took a firm hold on the show. Thurston now gets his orders from The Bureau, presumably a government agency but its origin and purpose are kept delibrately shrouded. Thurston's "sidekick"/comic relief/sometime nemesis, Egon Zellschmidt, originally played by Hans Conried in the first season, is now played by Leon Belasco. Zellschmidt, a rogue of the first order, usually happens to show up wherever Thurston is sent, supposedly visiting one of his many cousins. Throughout the series Zellschmidt's first name changes from Egon to Zegon, Agon, or Pegon -- whichever name suits his particular purpose at the moment.
The Man Called X ran through May 1952 -- a total of 227 episodes, of which perhaps eighty survive. The show was later adapted for television, running in the 1956-1957 season (39 episodes) and starred Barry Sullivan as Thurston.
"The Plot To Kill a NATO Project" aired on March 11, 1952 and takes place in Lisbon.