Pope Leo XIII, born Vincenzo Gioacchino Pecci on March 2, 1810, in Carpineto Romano, Italy, served as the 256th pope of the Roman Catholic Church from 1878 until his death on July 20, 1903, at age 93.[1][2][3] The oldest pope at election, he was a diplomat, scholar, and reformer who succeeded the tumultuous reign of Pius IX, restoring stability to the Church amid the loss of the Papal States in 1870.[1][2] Before his papacy, Pecci excelled as a civil servant, legate in Benevento and Spoleto, and archbishop of Perugia from 1846 to 1878, where he built homeless shelters, soup kitchens, reformed taxes, and aided earthquake victims, donating his 1853 cardinal elevation funds to flood relief.[1][3][4] Elevated to cardinal in 1853, he modernized seminaries, revived Thomist theology, and founded charitable institutions.[3][4] As pope, Leo XIII bridged faith and modernity, re-founding the Vatican Observatory and affirming science-religion harmony.[1][5][6] Known as the "Rosary Pope," he issued eleven encyclicals on the rosary and approved new Marian scapulars.[2][6] His landmark 1891 encyclical *Rerum Novarum* championed workers' rights, just wages, unions, and private property while critiquing socialism and unchecked capitalism, founding Catholic Social Teaching.[5][7][8] A skilled diplomat, he improved ties with Russia, Germany, France, Britain, Italy, the U.S., Brazil, and Eastern Orthodox churches, opened Vatican Archives in 1883, and created 248 new dioceses.[1][2][4] He promoted Marian devotion, education, and aid for the poor, including a Vatican hospice during the 1891 cholera pandemic.[2][6] Leo XIII's intellectual legacy endures in social justice doctrine, Church-world engagement, and Thomism's revival, positioning the Church as a mainstream European force despite lacking temporal power.[1][2][5] His remains rest in the Archbasilica of Saint John Lateran.[2]