GREGORY IX. (Ugolino Conti de Segni), pope from March 19, 1227, to Aug. 22, 1241, was a nobleman of Anagni and probably a nephew of Innocent III. He studied at Paris and Bologna, and, having been successively archpriest of St. Peter's, papal chaplain, cardinal-deacon of Sant' Eustachio, cardinal-bishop of Ostia, first protector of the Franciscans, and papal legate in Germany under Innocent III. and Honorius III., succeeded the latter in the papacy. On Sept. 29, 1 227, he excommunicated the emperor Fred erick II. for continued neglect of his vows and refusal to under take the crusade. When Frederick finally set out the following June without making submission to the pope, Gregory raised an insurrection against him in Germany, and forced him in 123o to beg for absolution. The Romans, however, disapproved of the temporal power and exiled the pope (June 1, 1231). Hardly had this contest been brought to an end favourable to the papacy (May 1235) when Gregory came into fresh conflict with Frederick II. He again excommunicated the emperor and released his sub jects from their allegiance (March 24, 1239). Frederick, on his side, invaded the Papal States and prevented the assembling of a general council convoked for Easter 1241.
Gregory systematized the Inquisition and entrusted it to the Dominicans. He supported Henry III. against the English barons, and protested against the Pragmatic Sanction of Louis IX. of France. He sent monks to Constantinople to negotiate for church unity, but without result. He permitted free study of Aristotle, and issued (1234) an important new compilation of decretals which he prescribed in the bull Rex pacificus should be the stand ard text-book in canon law at Bologna and Paris. Gregory was famed for his learning, his blameless life, and his strength of character. He died on Aug. 22, 1241, while Frederick II. was ad vancing against him.
For his life see his Letters in Monumenta Germaniae historica (1883) ; "Les Registres de Gregoire IX.," ed. L. Auvray in Bibiiotheque des ecoles f rancaises d'Athenes et de Rome (1890 seq.) ; A. Potthast, Regesta pontif. Roman. (1875) and "Registri dei Cardinali Ugolino d' Ostia et Ottaviano degli Ubaldini," ed G. Levi in Fonti per la storks d' Italia (189o). See J. Felten, Papst Gregor IX. (Freiburg i. B., 1886) ; J. Marx, Die Vita Gregorii IX. (1889) ; P. Balan, Storia di Gregorio IX. (3 vols., Modena, 1872) ; T. Frantz, Der grosse Kampf zwischen Kaisertum u. Papsttum zur Zeit des Hohenstaufen Friedrich II. (i9o3) ; W. Norden, Das Papsttum u. Byzanz (19o3) , and bibliography in Herzog-Hauck's Realencyklopddie.