Gregory IX, originally Ugo or Ugolino de Segni 1148/55-1241
Italian pope

He was the nephew of Pope Innocent III, by whom he was created cardinal-deacon in 1198. A strong supporter of the Franciscans and the Dominicans, he became pope in 1227 and constantly feuded with Emperor Frederick II, of Germany, asserting the supremacy of papal power. After a phase of uneasy collaboration with the emperor, in which the pope supported him in his relations with the Lombard cities, while he supported the pope against opposition in Rome, a ferocious conflict broke out over Frederick's Constitutions of Melfi which subjected Sicily to his will. Rome itself was under siege when the pope died. He was responsible for ordering the first authoritative collection of papal decretals (1234), which were to remain the basic source of canon law in the Catholic Church until 1917.