(1852–1914), born in Curaçao, graduated from Columbia University and became a leader of the Socialist Labor party, editing its journal, The People. After some of his party's members joined Debs to found the Socialist Democratic party (later Socialist party) in 1899, De Leon helped to organize the I.W.W. and later promoted a rival group to work for industrial unionism. His major pamphlet is Socialist Reconstruction of Society (1905) and he also translated most of Eugène Sue's series The Mysteries of the People.
From The Oxford Companion to American Literature in Oxford Reference.