https://en.wikipedia.org/wiki/Hermann_Billung

Hermann Billung was the Margrave of the Billung March from 936 until his death. The first of the Saxon House of Billung, Hermann was a trusted lieutenant of Otto I, Holy Roman Emperor.

Though never Duke of Saxony himself, while Otto was in Italy from 961 until 972, Hermann served as Otto's personal representative in governing Saxony. Towards the end of his life, Hermann was the effective Duke in all but name.

Hermann died in 973, just two months before Otto's own death. Hermann's son Bernard I was named as the new Duke of Saxony by Otto I's son Otto II, the new Holy Roman Emperor.