Daniel De Leon

Socialist advocate, born on the island of Curaçao, Netherlands Antilles. He studied in Europe before emigrating to New York City (1874), becoming a lawyer (1878) and lecturer on Latin-American diplomacy at Columbia University (1883–6). Joining the Socialist Labor Party (1890), he was named its national lecturer (1891) and editor of its organ, The People (1892), and was an unsuccessful candidate for governor and Congress. A lifelong leader of the party, antagonistic to existing trade unions, his intrangiency eventually led to formation of a splinter group, the Socialist Party of America. In 1905 he also assisted in the formation of the Industrial Workers of the World (IWW), which soon fragmented. He was ousted from the IWW and formed his own Workers' International Industrial Union. To opponents he was a disruptive fanatic, but to supporters a man of incorruptible integrity. Lenin praised his writings as incorporating the germ of the Soviet system.

Daniel De Leon (December 14, 1852 – May 11, 1914) was a Curaçao-born American socialist and Syndicalism-influenced trade unionist of Jewish origin.

De Leon settled in New York City, studying at Columbia University.

De Leon was a Marxist, and argued for the revolutionary overthrow of capitalism, trying to divert the SLP away from its Lassallian outlook.

De Leon was highly critical of the trade union movement in America and described the craft-oriented American Federation of Labor as the American Separation of Labor. At this early stage in De Leon's development there was still a considerable remnant of the general unionist Knights of Labor in existence, and the SLP worked within it until driven out.

By the early 20th century the SLP was declining in influence, with first the Social Democratic Party and then the Socialist Party of America becoming the leading leftist political force in America. However, De Leon remained an important figure in the US labor movement, and in 1905 he helped found the Industrial Workers of the World (IWW).

De Leon lost control and the ability to influence the organisation to what he called disparagingly 'the bummery'. De Leon was engaged in a policy dispute with the leaders of the IWW. His argument was in support of political action via the Socialist Labor Party while other leaders, including founder Big Bill Haywood, argued instead for Direct Action. Haywood's faction prevailed and De Leon left the IWW to form a rival Detroit-based IWW, which was soon renamed as the Workers' International Industrial Union.

Daniel De Leon proved hugely influential to other socialists, also outside the USA.

De Leon's brand of Marxism is known as Marxism-Deleonism or simply as De Leonism.