The Panhellenic Socialist Movement, known mostly by its acronym PASOK, was a social-democratic political party in Greece. Following the collapse of the Greek military dictatorship of 1967–1974, PASOK was founded on 3 September 1974 as a socialist party by Andreas Papandreou. The largest left-of-center party in Greece between 1977 and 2012, it was the dominant political party of the country from 1981 to 2004, under party founder Andreas Papandreou and Costas Simitis. After the Metapolitefsi and until 2012 it was one of the two major parties in the country, along with New Democracy, its main political rival.