(party pseudonym, Sewer). Born Dec. 4, 1888, Puławy; died Aug. 21, 1937. Leader in the Polish and international labor movement.
Próchniak joined the Social Democracy of the Kingdom of Poland and Lithuania (SDKPL) in 1903 and the Communist Party of Poland (CPP) in December 1918. He took part in the revolutionary actions of the workers in the Dąbrowa coal basin from 1905 to 1907 and was repeatedly arrested and exiled for his revolutionary activities. In 1911 he studied at the Party School in Longjumeau, near Paris, which was headed by V. I. Lenin.
A co-founder of the Moscow group of the SDKPL in 1917–18, Próchniak took an active part in the October Revolution of 1917 and was a member of the Lefortovo-Blagusha Raion Committee of the Bolshevik Party. Próchniak lived in Warsaw in 1918–19, serving as secretary of the military section of the Central Committee of the CPP. In 1920 he was in Białystok as a member of the Provisional Revolutionary Committee of Poland and of the Polish Bureau of the Central Committee of the RCP (Bolshevik). Próchniak attended the Second through Sixth Congresses of the CPP. From 1925 he was repeatedly elected to the Politburo of the Central Committee of the CPP; he was a candidate member of the Politburo from 1931 to 1937.
As the CPP’s representative on the Executive Committee of the Comintern from 1921, Próchniak attended the Fourth through Seventh Congresses of the Comintern. He was elected a member of the Executive Committee of the Comintern in 1922, a member of the Executive Committee’s Presidium in 1928, and a candidate member of the Executive Committee of the Comintern in 1935.