Pope Innocent III (Latin: Innocentius III; not to be confused with Antipope Innocent III) reigned from 8 January 1198 to his death in 1216. His birth name was Lotario dei Conti di Segni, sometimes anglicised to Lothar of Segni.
Pope Innocent was one of the most powerful and influential popes. He exerted a wide influence over the Christian states of Europe, claiming supremacy over all of Europe's kings. Pope Innocent was central in supporting the Catholic Church's reforms of ecclesiastical affairs through his decretals and the Fourth Lateran Council. This resulted in a considerable refinement of Western canon law. Pope Innocent is notable for using interdict and other censures to compel princes to obey his decisions, although these measures were not uniformly successful. Innocent called for Christian crusades against Muslim Spain and the Holy Land, as well as the Albigensian Crusade against the Cathars in southern France.
One of Pope Innocent's critical decisions was organizing the Fourth Crusade. Originally intended to attack Jerusalem through Egypt, a series of unforeseen circumstances led the crusaders to Constantinople, where they ultimately sacked the city in 1204. Although the attack went against his explicit orders, and the Crusaders were subsequently excommunicated, Innocent reluctantly accepted this result, seeing it as the will of God to reunite the Latin and Orthodox Churches. This particular conflict led to an increase of hostility between the two churches.