Pope Leo XIII (Italian: Leone XIII; born Gioacchino Vincenzo Raffaele Luigi Pecci; 2 March 1810 – 20 July 1903) was head of the Catholic Church from 1878 until his death in 1903. He had the fourth-longest reign of any pope, behind those of Peter the Apostle, Pius IX (his predecessor), and John Paul II.
Born in Carpineto Romano, near Rome, Leo XIII is well known for his intellectualism and his attempts to define the position of the Catholic Church with regard to modern thinking. In his 1891 encyclical Rerum novarum, Pope Leo outlined the rights of workers to a fair wage, safe working conditions, and the formation of trade unions, while affirming the rights to property and free enterprise, opposing both atheistic socialism and laissez-faire capitalism. With that encyclical, he became popularly called the "Social Pope" and the "Pope of the Workers", also having created the foundations for modern thinking in the social doctrines of the Catholic Church, influencing his successors. He influenced the Mariology of the Catholic Church and promoted both the rosary and the scapular. Upon his election, he immediately sought to revive Thomism, the theological system of Augustine of Hippo and Thomas Aquinas, wishing to make it the official political, theological, and philosophical foundation of the Catholic Church. As a result, he sponsored the Editio Leonina in 1879.