Gregory IX, 1143?–1241, pope (1227–41), an Italian named Ugolino di Segni, b. Anagni; successor of Honorius III. As cardinal under his uncle, Innocent III, he became, at St. Francis' request, the first cardinal protector of the Franciscans. About 84 when he was elected, he was a vigorous pope despite his age. He immediately commanded Holy Roman Emperor Frederick II to keep his vow to go on crusade and excommunicated (1227) him when he delayed. The imperialists in Rome forced (1228) the pope into exile until 1230, when emperor and pope were reconciled. Five or six years later the struggle broke out again, this time over Italian liberties. Gregory again excommunicated (1239) Frederick and ordered his dethronement. Frederick prevented circulation of the bulls in Germany and blocked a general council summoned by Gregory. Gregory died at 98 when Frederick was about to attack the city. He was succeeded by Celestine IV. Gregory ordered the first complete and authoritative collection of papal decretals, the Corpus Iuris Canonici, which remained a fundamental source of canon law until the promulagtion of the Codex Iuris Canonici in 1917. Gregory IX organized (1233) the Inquisition and gave special responsibility for it to the Dominicans.
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