Helmold of Bosau (c. 1120 – after 1177) was a Saxon historian of the 12th century and a priest at Bosau near Plön. He was a friend of the two bishops of Oldenburg in Holstein, Vicelinus (died 1154) and Gerold (died 1163), who did much to Christianize the Polabian Slavs. Source: Wikipedia (en)