In 1102, the emperor appointed and invested him as Bishop of Bamberg in Franconia, and Otto became one of the leading princes of medieval Germany. He consolidated his widely scattered territories and during his tenure as bishop, Bamberg rose to great prominence. In 1106 Otto received the pallium from Pope Paschal II. He achieved fame as diplomat and politician, notably during the Investiture Controversy between the emperor and the papacy. It was Bishop Otto, substituting the imprisoned archbishop Adalbert of Mainz, who clothed Hildegard of Bingen as a Benedictine nun at Disibodenberg Abbey about 1112. He remained loyal to the Imperial court and, as a consequence, was suspended by a papal party led by Cuno of Praeneste at the Synod of Fritzlar in 1118. At the Congress of Würzburg in 1121, Otto successfully negotiated the peace treaty, the Concordat of Worms, which was signed in 1122. In the 1130s, he continued to arbitrate between Emperor Lothair of Supplinburg and the rising Hohenstaufens. As bishop, Otto led a model, simple and frugal life, but did much to improve his ecclesiastical and temporal realms. He restored and completed Bamberg Cathedral after it had been damaged by fire in 1081, improved the cathedral school, established numerous monasteries and built a number of churches throughout his territory. He greatly expanded the town of Bamberg, rebuilding the Monastery of St. Michael, which had been destroyed by an earthquake around 1117.
Missionary
Among his great accomplishments was his peaceful and successful missionary work among the Pomeranians, after several previous forcible attempts by the Polish rulers and the Spanish bishop Bernard to convert Pomerania to Christianity had failed. Otto was sent on his first mission by the Polish duke Bolesław III Wrymouth in 1124. As the official papal legate, he converted a large number of Pomeranians, notably in the towns of Pyrzyce, Kamień, Szczecin, and Wolin, and established eleven churches, and became known as the "Apostle of Pomerania." After he returned to Bamberg in 1125, some pagan customs began to reassert themselves, and Otto journeyed once more to Pomerania in 1128. In the Diet of Usedom, he succeeded in converting all the nobles, converted further communities, and sent priests from Bamberg to serve in Pomerania. His intent to consecrate a bishop for Pomerania was thwarted by the bishops of Magdeburg and Gniezno who claimed metropolitan rights over Pomerania. Only after his death in 1139 was his former companion, Adalbert of Pomerania, consecrated as Bishop of Wolin, in 1140. Otto died on 30 June 1139, and was buried in Michaelsberg Abbey, Bamberg. He was canonised in 1189 by Pope Clement III. Although he died on 30 June, his name is recorded in the Roman martyrology on 2 July. The area of western Prussia around Gdańsk was Christianized via Pomerania as well, and the monastery of Oliwa at Gdańsk was established at that time, while eastern Prussia was Christianized later via Riga by the Teutonic Knights.
