Gregory IX (pope)

Gregory IX organized the papal Inquisition, handing the hunt for heresy to trained inquisitors, often Dominicans. He issued a major collection of church law, the Decretals, that stayed in force for centuries. He canonized his friend Francis of Assisi just two years after his death, and Anthony of Padua and Dominic as well. He spent much of his reign in a bitter feud with Emperor Frederick II, whom he excommunicated more than once.