Pelagius rose in the ranks of the clergy by serving as cardinal deacon, then priest, then bishop. He was in charge of the Church’s funds as an auditor (controlling accountant), and made efforts to unify the Roman and Greek Orthodox churches in the Latin Empire of Constantinople that was established after the Fourth Crusade and the sack of Constantinople. He tried to close Orthodox churches and imprison the priests but local resistance made this impossible.
He was appointed papal legate to the Fifth Crusade by Innocent III, where he was to reform the Eastern church and keep the peace after the expected victory. In 1218, he met the crusading army that was already besieging Damietta in Egypt. He differed with John of Brienne, King of Jerusalem, on strategy, and urged the army to continue the attack instead of negotiating. He believed it would be possible to take Cairo, and that Frederick II of Bavaria would become Emperor of Egypt.
After the defeat of the army under Pelagius, he was taken hostage until the Crusaders were granted safe passage to leave Egypt, and took much of the blame for the defeat, even though the shortage of funds, soldiers and the late arrival of Frederick II, as well as the Nile flood, were important to the defeat.
Pelagius remained an important figure in Outremer, or the Crusader States, resolving conflicts among leaders and branches of the Church, and planning further crusades and internal campaigns in the Mediterranean region among competing officials. John of Brienne became Latin Emperor of Constantinople, Frederick II returned victorious after concluding a treaty with al-Kamil that gave him temporary control of Jerusalem. Before his death in 1230, Pelagius conducted negotiations between Emperor Frederick II and Pope Gregory IX.
Sources: “Pelagius of Albano (d. 1230) – The Crusades.” http://erenow.com/postclassical/crusades/719.html; “Cardinal Pelagius | Project Gutenberg Self-Publishing – EBooks | Read EBooks Online.” http://www.gutenberg.us/articles/cardinal_pelagius.