Giacomo Antonelli was an Italian cardinal deacon. He was the Cardinal Secretary of State from 1848 until his death; he played a key role in Italian politics, resisting the unification of Italy and affecting Roman Catholic interests in European affairs. He was often called the "Italian Richelieu" and the "Red Pope."

The Secretary of State of His Holiness, known as the Cardinal Secretary of State, presides over the Holy See's Secretariat of State, which is the oldest and most important dicastery of the Roman Curia. The Secretariat of State performs all the political and diplomatic functions of the Holy See and the Vatican City State. The secretary of state is sometimes described as the prime minister of the Holy See, even though the nominal head of government of Vatican City is the President of the Pontifical Commission for Vatican City State.