Mieczysław Moczar (Polish pronunciation: [mjɛˈt͡ʂɨswaf ˈmɔt͡ʂar]; original name Mikołaj Diomko, pseudonym Mietek, December 23, 1913 in Łódź – November 1, 1986) was a Polish communist who played a prominent role in the history of the Polish People's Republic. He is known for his ultranationalist, xenophobic and antisemitic attitude which influenced Polish United Workers' Party politics in the late 1960s. During this time, General Moczar and his supporters challenged general secretary Władysław Gomułka's authority.
He was heavily involved in the so-called March 1968 events in Poland against Polish Jews, in which he led the faction of hardliners inside the Communist Party.
Moczar was a member of the Communist Party before World War II. During the occupation, Moczar organized communist guerillas in the Lublin and Kielce regions. His active role in the Communist underground during the resistance allowed him to become known as "the leader of Poland's 'Partisans'" in the 1960s. Immediately following World War II, Moczar became the secret police chief in Łódź, but was dismissed from his position in 1952 on charges of "nationalist deviation." During this "period of widespread suspicion against the self-made Communist veterans of the Communist resistance," Moczar was briefly held in detention. When Władysław Gomułka returned to power as the First Secretary of the Polish United Workers' Party in 1956, Moczar started to work for the Interior Ministry.