Nicholas III, né Giovanni Gaetano Orsini (ca. 1216 - August 22, 1280), pope from November 25, 1277 to his death in 1280, was a Roman nobleman who had served under eight popes, been made cardinal-deacon of St Nicola in carcere Tulliano by Pope Innocent IV, protector of the Franciscans by Pope Alexander IV, inquisitor-general by Pope Urban IV, and succeeded Pope John XXI, largely through family influence, after a six-months' vacancy in the Holy See. His brief pontificate was marked by several important events. A born politician, he greatly strengthened the papal position in Italy. He concluded a concordat with Rudolph I of Habsburg in May 1278, by which the Romagna and the exarchate of Ravenna were guaranteed to the pope; and in July he issued an epoch-making constitution for the government of Rome, which forbade foreigners taking civil office. Nicholas issued the bull Exiit on 14 August 1279 to settle the strife within the Franciscan order between the parties of strict and loose observance. He repaired the Lateran palace and the Vatican at enormous cost, and erected a beautiful country house at Soriano near Viterbo. Nicholas, though a man of learning noted for his strength of character, brought just reproach on himself for his efforts to found principalities for his nephews and other relations. He died of a heart attack.

Dante in The Inferno from The Divine Comedy talks briefly to Pope Nicholas III, who was condemned to spend eternity in the Eighth Circle, Third Bolgia of Hell, reserved for Simoniacs.