Nicholas George Shadrin, born Nikolai Fedorovich Artamonov, was a Soviet Naval officer who defected to the United States of America in 1959.
He worked for CIA and was engaged in various counter-intelligence assignments during the cold war. He was allegedly kidnapped by KGB agents while in Vienna with his wife. Another Soviet defector revealed, at a later date, that Shadrin had died from an overdose of chloroform during the operation.
http://www.mitchellspublications.com/ur/loc/hurth/sha/index.htm
http://www.cnn.com/SPECIALS/cold.war/episodes/21/spotlight/
Soviet Defectors The KGB Wanted List, By Vladislav Krasnov
Shadrin, the Spy Who Never Came Back, By Henry Hurt, Reader's Digest Press, 1981