ALEXANDER IV (Rinaldo) (?-May 25, 1261, pope from 1254, was, like Innocent III and Gregory IX, a member of the family of the counts of Segni. His uncle Gregory IX made him cardinal deacon in 1227 and cardinal bishop of Ostia in 1231. On the death of Innocent IV he was elected pope at Naples on December 12, 1254. He is described as a stout man, kindly, cheerful, but of no great brilliancy. He succeeded Innocent IV as guardian of Conradin, the last of the Hohenstaufen, promising him his benevolent protection; but in less than a fortnight he conspired against him and bitterly opposed Conradin's uncle Manfred. Alexander fulminated with excommunication and interdict against the party of Manfred, but in vain; nor could he enlist the kings of England and Norway in a crusade against the Hohenstaufen. Rome itself became too Ghibelline for the pope, who withdrew to Viterbo, where he died in 1261. His pontificate was signalized by efforts to unite the Eastern Orthodox and Roman Catholic churches, by the establishment of the Inquisition in France, by favours shown to the mendicant orders, and by an attempt to organize a crusade against the Tatars.

Reference

Also see...

Preceded by:
Pope Innocent IV
List of popes Succeeded by:
Pope Urban IV