Marcin Jerek is a Polish-born American citizen who was once an interrogator for the CIA and who lectured on interrogation techniques at Langley, until health complications forced him into retirement. During the 1980's, he was attached to a joint British-American task force in Afghanistan that also included the young Dr. Donald Mallard. Mallard confided to Leroy Jethro Gibbs that Jerek was incapable of feeling any physical pain, a condition which either made him indifferent to his victims' suffering, or else drove him to use torture as a means of "experiencing" pain by proxy.