Andreu Nin i Pérez (1892–1937) was a Catalan politician, trade unionist and translator. He is mainly known for his role in various Spanish left-wing movements of the early 20th century and, later, for his role in the Spanish Civil War. He is also known for his work translating Russian classics such as Ana Karenina, Crime and Punishment and some works by Anton Chekhov, from Russian into Catalan.

The Workers' Party of Marxist Unification was a Spanish communist party formed during the Second Republic and mainly active around the Spanish Civil War. It was formed by the fusion of the Trotskyist Communist Left of Spain and the Workers and Peasants' Bloc against the will of Leon Trotsky, with whom the former broke.