Alexander Danieliuk-Stefanski (also Stefański or Ștefanski; 30 November 1897, Warsaw – 21 August 1937, Moscow) was a Polish communist politician, active in Poland and in the Soviet Union. From 1931 to 1936, he oversaw the activities of Romanian communists in exile to the Soviet Union, and served as General Secretary of the Romanian Communist Party (PCdR). During the period, he was seconded by Elena Filipescu, who was also his lover.