"John I, Count of Oldenburg (c. 1204 – c. 1270) was a ruling Count of Oldenburg from 1233 until his death.
His father, Christian II, had ruled jointly with his uncle, Otto I. After Christian II died in 1233, Otto I acted as guardian for the underage John I. When John I came of age, he ruled jointly with Otto I. After Otto I died in 1251, John I ruled alone.
In 1244, Otto I and John I together founded the Cistercian Rosenthal monastery in Menslage. In 1251, the monastery moved to a fort in the Börsteler Forest, which John I already owned.
In 1258 and 1259, he fought in the Bremen Prince-Archbishopric Feud on the side of his cousin Hildebold of Wunstorf against Rüstringen, Östringen and Stedingen. When the feud had ended, he kept the territories he had conquered." - (en.wikipedia.org 02.01.2021)
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