Charles Ruthenberg (July 14, 1884 – 1927) became famous for founding the Communist Party in the USA.

Ruthenberg was born in New York City, New York, the son of an immigrant from Russia who was a prosperous garment merchant. He entered Columbia University in 1903, where he became involved with anarchist groups and became a member of a radical wing of the Socialist Party USA. He became an avid pamphlet writer during this period and was a head of a student group that actively supported the election of Eugene Debs for president in 1904.

Ruthenberg graduated from Columbia Law School in 1909, and struggled with an independent law practice, while also active in the SPUSA as a pamphleteer and activist. Between the years 1910 and 1919, Ruthenberg went to many cities in the American northeast and midwest, speaking to labor groups, union organizers, antiwar groups and the like and ran as the Socialist Party candidate for the Senate from Ohio in 1916 and for Mayor of Cleveland in 1917.

He was imprisoned, along with Alfred Wagenknecht and Charles Baker , in 1918 on charges of obstructing registration for the draft by calling for a general strike to oppose the United States' entry into World War I. Debs' speech to a rally in Canton, Ohio condemning the war and the persecution of Ruthenberg, Wagenknecht and Baker eventually resulted in his conviction for violating the Espionage Act. Ruthenberg was later convicted of assault in connection with the death of a police officer at a May Day rally in Cleveland in 1919.

He led one of two groups which split from the SPUSA in 1919 and which later, at the command of the Comintern, merged to form the Communist Party USA. The group that he headed, known as the Communist Party of America before the merger, was dominated by the foreign language federations that provided most of the CPUSA's members at that time.

The forced merger did not, however, end the rivalries between the two groups. Ruthenberg and his supporter Jay Lovestone were at odds with a rival faction led by William Z. Foster, who had strong ties to organized labor and who wanted to direct the party's work toward organizing within the American-born working class, and James P. Cannon, who led the International Labor Defense organization.

Ruthenberg, wife Evelyn and their son Eugene traveled to the Soviet Union from 1921 to 1924, where he worked in a tractor and agricultural equipment factory in Moscow and studied Russian at Moscow State University. He ran unsuccessfully for a seat in the House of Representatives from Ohio's 20th Congressional District as the candidate of the Workers Party, as the CPUSA was then known, on his return to the United States.

In 1925 Comintern representative Sergei Gusev ordered the majority Foster faction to surrender control to Ruthenberg's faction; Foster complied. The factional infighting within the CPUSA did not end, however; the communist leadership of the New York locals of the International Ladies' Garment Workers' Union lost the 1926 strike of cloakmakers in New York City in large part because of intra-party factional rivalries, as neither group wanted to take the responsibility for accepting a strike settlement that appeared insufficiently revolutionary.

Ruthenberg died in 1927. He was buried, as was his former rival John Reed, in the Kremlin's wall.