Paul Singer (1932-2018) was most of his life a direct part of the twentieth-century social movements and those at the beginning of the twenty-first century. He is one of the most renowned and respected democratic left-wing activists of his time in Brazil. Paul Singer was born in Vienna (Austria) in a Jewish family, and he went to Brazil at 8 years old in 1940, escaping from the Nazis. He started his political education when he was a young boy. By the end of Getulio Vargas’ dictatorship in 1945, the Brazilian Communist Party was legally registered and attracting a large part of the country’s left-wing activists. Singer discovers that many of his friends are communists, but he decides to join the socialists, opposing the Stalinists. At the age of 15, he discovers a text from Rosa Luxemburg on the Russian Revolution (Luxemburg 2008). From then on, Rosa Luxemburg becomes a frequent reference for Singer’s activism and intellectual reflections, making him one of the first “Luxemburgists” in the country.