 Wichmann in turn joined the unsuccessful rebellion of King Otto's half-brother Thankmar and Duke Eberhard of Franconia in 938.Having more autonomy than the contemporary margrave Gero ruling over the adjacent "Marca Geronis" in the south, Hermann exacted tribute from the local Polabian Slavs of the Obotrite tribal federation.Upon his brother's death in 944, he also became count in the Saxon Bardengau around the town of Lüneburg, where he founded the monastery of St Michael in that city.