(5 Feb. 1265–29 Nov. 1268)
On Urban IV's death the cardinals at Perugia were so sharply divided that they took four months to elect a successor. He was another Frenchman, Guy Foucois, son of a successful judge, born c.1195 at Saint-Gilles-du-Gard. After studying law at Paris, he became legal consultant to Count Raimund VII of Toulouse and later to King Louis IX (1226–70). His frequent encounters with the inquisition in his capacity as a lawyer led him to write a manual for inquisitors, Questiones quindecim ad inquisiores. He married and had two daughters, but after his wife's death became a priest c.1256 and served as archdeacon of Le Puy. His promotion was rapid: bishop of Le Puy in 1257, archbishop of Narbonne in 1259, Urban IV created him cardinal bishop of Sabina against his wishes on 24 Dec. 1261, and in Nov. 1263 sent him as legate to England to support Henry III (1216–72) against the barons. Elected in absence while travelling home, he had to come to Perugia disguised as a monk because of hostile conditions in north Italy. As pope he resided, again because of the hostile atmosphere in Rome, first at Perugia and then at Viterbo.
A legalist, more timid than Urban IV, he completed Urban's policy of excluding the Hohenstaufen dynasty from Italy and installing Charles, count of Anjou (1226–85), as king of Sicily and Naples in place of Manfred (c.1232–66), Emperor Frederick II's bastard son. Fearing that Manfred would seize Rome, he put pressure on Charles, who reached the city in May 1265, where on 28 June five cardinals commissioned by the pope invested him with the southern kingdom. With much heart-searching Clement now helped him to borrow vast sums, secured by a 30-year tithe on the French church, from Tuscan bankers to finance the Sicilian campaign he was pledged to undertake. A crusade had been preached against Manfred in France, and a powerful French army moved to the frontier of the kingdom. The decisive battle was fought at Benevento on 26 Feb. 1266 and resulted in Manfred's defeat and death. His new realms now lay open to Charles, but two years later, on the crest of a reaction against the excesses of his rule, the last of the Hohenstaufen, the youthful Conradin, duke of Swabia and king of Jerusalem, marched to Italy to win back his imperial heritage. In the interregnum in Germany Clement had forbidden his election as king, and now tried to halt his advance by excommunicating him and his adherents, and deposing him from the throne of Jerusalem. Conradin was rapturously received in Rome in July 1268, but on 23 Aug. was defeated by Charles at Tagliacozzo (prov. of L'Aquila) and himself captured and, after trial, beheaded. Clement did nothing to prevent this unworthy act; he had deliberately appointed Charles imperial vicar in Tuscany on 17 Apr., an office which gave him legal power to execute the young prince as a disturber of the peace.
The papacy had gained its objectives, but its triumph was mixed with disillusion. Whereas its aim had been that the new lord of Sicily should be confined to his kingdom, Clement had to acquiesce in the predominance Charles had acquired for himself in central and north Italy and in the papal state itself; when the threat of Conradin loomed, he even found himself appointing his young vassal to positions of immense authority in Italy undreamed of in the original treaty. He had got rid of the Hohenstaufen, only to find that the Angevin house was as great a threat to the independence of the holy see.