Pope Pius XII, photographed in 1938 by Ernest Nash. Pius XII, born Eugenio Maria Giuseppe Giovanni Pacelli (1876-1958), reigned as Pope, head of the Catholic Church and sovereign of Vatican City State, from 1939 until his death in 1958. One of the most influential popes in the history of the Catholic church, Pius IX is remembered chiefly as the pontiff who advocated the concept of papal infallibility and proclaimed the dogma of Immaculate Conception. In modern times Pius IX has been accused of anti-Semitism, based on his policies toward Roman Jews. He was beatified in 2000 by Pope John Paul II.