Among Indonesia's movements of Islamic reform, Persatuan Islam (Islamic Union, or Persis) has been the most puritan in doctrine and practice and the most polemical opponent of traditionalist Islam and local religious practices. Although much smaller than better-known movements such as Muhammadiyah and Sarekat Islam, Persis has had an influence far out of proportion to its modest size because of the intensity of its message and the forceful personalities of its leaders. Its leading intellectual, Mohamad Natsir, became one of the first prime ministers of independent Indonesia; went on to lead the largest Muslim party, Masyumi, until it was banned in 1960; established the Indonesian Council for Islamic Predication (daעwa); and was for many years one of the vice-chairmen of the Islamic World League. As the most rigid and literalist of the reformist currents, as well as the most polemical, Persis often set the terms of the debate with traditionalists and syncretists, and the numerous fatwas issued by its ulema were often used as a reference by the followers of other reformist currents.