Pius IX

Pius IX was pope from 1846 to 1878, making him the longest-serving pope in history. He is known for defining and promoting several key doctrines of the Catholic Church, including the Immaculate Conception of Mary. His papacy coincided with significant social and political changes in Europe, leading him to become more conservative and resistant to modernity. Pius IX convened the First Vatican Council in 1869, which affirmed the doctrine of papal infallibility, stating that the pope cannot err when teaching on faith and morals. His reign was marked by both spiritual leadership and political challenges.