Joan Comorera i Soler was a Spanish Communist politician, journalist and writer from Catalonia who spent several years in Argentina before returning to Spain in 1931 at the start of the Second Spanish Republic. He was a Catalan nationalist, and was elected chairman of the Socialist Union of Catalonia in 1933. In 1936 he became Secretary General of the Unified Socialist Party of Catalonia (PSUC), in alliance with the Spanish Communist Party. During the Spanish Civil War (1936–1939) he built up his party into a major political force during the struggles among the supporters of the Republic between Socialists, Stalinists, Trotskyists and Anarcho-syndicalists. After the Republicans were defeated by the right-wing forces led by Francisco Franco he went into exile, living in Mexico and then in France. In 1949 he was expelled from the Communist party for his Catalan nationalism, and survived an assassination attempt. In 1951 he moved back to Catalonia using a false name. He was arrested in 1954 and died in prison four years later.

The Unified Socialist Party of Catalonia was a communist political party active in Catalonia between 1936 and 1997. It was the Catalan branch of the Communist Party of Spain and the only party not from a sovereign state to be a full member of the Third International.