Pope Pius XI, born Ambrogio Damiano Achille Ratti, was the Bishop of Rome and supreme pontiff of the Catholic Church from 6 February 1922 to 10 February 1939. He also became the first sovereign of the Vatican City State upon its creation as an independent state on 11 February 1929. He remained head of the Catholic Church until his death in February 1939. His papal motto was "Pax Christi in Regno Christi", translated as "The Peace of Christ in the Reign of Christ".

Vatican City, officially the Vatican City State, is a landlocked sovereign country, city-state, microstate, and enclave within Rome, Italy. It became independent from Italy in 1929 with the Lateran Treaty, and it is a distinct territory under "full ownership, exclusive dominion, and sovereign authority and jurisdiction" of the Holy See, itself a sovereign entity under international law, which maintains the city-state's temporal power and governance, diplomatic, and spiritual independence. The Vatican is also a metonym for the pope, Holy See, and Roman Curia.