Olof (Old Norse: Óláfr) was a Swedish monarch or local ruler who ruled over Birka, an important port town, and possibly Uppsala, an important early Swedish political center, in about 852, when the Catholic missionary Saint Ansgar made his second voyage from Germany to Birka in about the year 851 or 852 A.D. He had an ambivalent attitude to Christianity, and was known as a successful warrior king in the Baltic region. Olof is not mentioned in the Icelandic sagas of the 12th and 13th century, which give a different line of succession of supposed Viking Age Swedish rulers, but the Vita Ansgari, the near-contemporary writings of Ansgar's companion Rimbert, and the 10th-century account of Adam of Bremen both mention him and are generally seen as more reliable than the sagas. Religious dispositions Ansgar had undertaken missionary work among the Swedes in 829-831, and laid the foundations to a fragile congregation based in the important merchant town Birka. By the early 850s Ansgar, who was now Archbishop of Hamburg-Bremen, began to worry about the future of the community which was without a priest. He received the consent of the East Frankish ruler Louis the German to go to Sweden in person and received a personal letter to the Swedish king Olof. When he came to Denmark, King Horik I provided him with an envoy and a message which asked Olof to allow Ansgar to missionise freely. Ansgar's biographer Rimbert, in his Vita Ansgari (Life of Ansgar) relates that the Archbishop arrived to Birka after having sailed for 20 days. The year is not certain but seems to have been 851 or 852. There he found that King Olof and a large part of the people were affected by a pagan counter-movement. A seer asserted that he had participated in the council of the Aesir who had expressed their dissatisfaction with the Christian god. In case the current gods were not sufficient to the people, the gods decided to accept the former King Eric (Erik Björnsson, or Erik Refilsson?) in their abode. The seer's vision was widely believed, a sanctuary was built in the honour of the long-deceased Eric, and people performed sacrifices to him. Having installed himself in Birka, Ansgar invited King Olof to his place and feted him with a meal and gifts. The king announced that he would be glad to assist Ansgar, but dared not undertake anything