Stjepan Mesaros, best known as Steve Nelson (1903–1993), was a Croatian-born American political activist. Nelson achieved public notoriety as the political commissar of the Abraham Lincoln Brigade in the Spanish Civil War and a leading functionary of the Communist Party, USA. Nelson is best remembered for having been prosecuted and convicted under the Smith Act in 1953.
https://en.wikipedia.org/wiki/Steve_Nelson_(activist)