Jean-Laurent-Frederick Longuet (Johnny) (1876-1938) was a French socialist and Karl Marx's grandson.
Son of Charles and Jenny Longuet. French lawyer and Socialist who in the First World War held a pacifist position but invariably voted for war credits. Founder and editor of the newspaper Le Populaire. At the Strasbourg Congress in 1918 his policy was adopted by the majority of the French Section of the Workers' International (SFIO) socialist party. After the Tours Congress of 1920 where the Communists gained the majority he supported the minority and joined the centrist Two-and-a-half International (the Vienna Union). He criticized the League Against Imperialism created in 1927 and supported by the Comintern. (Source: Marxist Internet Archive)