Louis the German
During the years 838–839, Otgar supported Louis the Pious against his son Louis the German who was in rebellion and trying to get all of East Francia under his control. He remained strongly opposed to the younger Louis even after the elder's death in 840. He supported Lothair I in the civil war that lasted until 843. In 842, he even tried to prevent Louis the German from meeting Charles the Bald and allying with him against Lothair. When Otgar finally died, Louis's hold on East Francia strengthened under his successor, Rabanus Maurus.