Sebald Justinus Rutgers (1879–1961) was a Dutch Marxist theoretician and journalist who played an important role in the Left Wing section of the Socialist Party of America. He was also a construction engineer who was active in building industry in the Soviet Union.
S. J. Rutgers was born in Leiden, Netherlands on January 25, 1879. He studied from 1896 to the Polytechnical School of Delft, where he came into contact with socialism. In 1900 he graduated as a civil engineer and took a job for the municipality of Rotterdam, where he worked on the expansion of the port. At the same time, he was active from 1899 in the SDAP. From 1911 to 1915 he was director of public works in Medan, and then buyer for Indonesian companies in the United States.
During World War I, Rutgers was a frequent contributor to the Left Wing socialist press in America. His influential articles in The International Socialist Review and other publications supported the antimilitarist Zimmerwald Left movement and helped publicize the ideas of revolutionary socialism to an American audience. Rutgers was the financial force behind the establishment of a group called the Socialist Propaganda League of America in 1915, a revolutionary socialist forerunner of the Communist Party of America.