Pope Leo XIII, born Gioacchino Vincenzo Raffaele Luigi Pecci on March 2, 1810, was the head of the Roman Catholic Church from February 20, 1878, until his death on July 20, 1903

. He had the fourth-longest papacy in history and was known for his intellectualism and efforts to reconcile the Church with modern thought

. He is especially famous for his 1891 encyclical Rerum novarum , which addressed the rights of workers to fair wages, safe conditions, and the formation of trade unions, while also affirming property rights and opposing both atheistic socialism and unregulated capitalism. This earned him the nicknames "Social Pope" and "Pope of the Workers," and laid the foundation for the Catholic Church's modern social doctrine

. Leo XIII promoted the revival of Thomism (the theological system of Thomas Aquinas), encouraged Marian devotion, and issued a record eleven encyclicals on the rosary

. He was the first pope not to have ruled the Papal States, which had been lost by 1870, and he sought to address the Church's loss of temporal power while maintaining its spiritual mission

. He also improved the Church's relations with civil governments, took a more conciliatory stance toward scientific progress, reformed clergy education, and reorganized the Vatican to be more efficient and frugal

. His diplomatic efforts helped heal estrangement between the Church and some governments, notably in Germany

. Pope Leo XIII died at age 93, the oldest pope to date, and was buried in the Vatican before his remains were moved to the Archbasilica of Saint John Lateran

. In summary, Pope Leo XIII was a reform-minded, intellectual pope who significantly shaped Catholic social teaching, promoted harmony between faith and reason, and worked to modernize the Church’s role in a changing world