- Italian ecclesiastic: pope 1846–78.
- original name Giovanni Maria Mastai-Ferretti. 1792–1878, Italian ecclesiastic; pope (1846–78). He refused to recognize the incorporation of Rome and the Papal States in the kingdom of Italy, confining himself to the Vatican after 1870. He decreed the dogma of the Immaculate Conception (1854) and convened the Vatican Council, which laid down the doctrine of papal infallibility (1870)
