Otto inherited the Duchy of Saxony and the kingship of the Germans upon his father's death in He continued his father's work of unifying all German tribes into a single kingdom and greatly expanded the king's powers at the expense of the aristocracy.
Through strategic marriages and personal appointments, Otto installed members of his family in the kingdom's most important duchies. This reduced the various dukes, who had previously been co-equals with the king, to royal subjects under his authority. Otto transformed the church in Germany to strengthen royal authority and subjected its clergy to his personal control. After putting down a brief civil war among the rebellious duchies, Otto defeated the Magyars at the Battle of Lechfeld in , thus ending the Hungarian invasions of Western Europe.
By , Otto had conquered the Kingdom of Italy. Otto's later years were marked by conflicts with the papacy and struggles to stabilize his rule over Italy. Reigning from Rome, Otto sought to improve relations with the Byzantine Empire , which opposed his claim to emperorship and his realm's further expansion to the south. Otto finally returned to Germany in August and died at Memleben in May Otto II succeeded him.
Otto has been consistently depicted in historiography through different eras as a successful ruler. He is also reputed to be a great military commander, especially on the strategic level [ 4 ] — this also means that the empire this talent recreated was too vast for contemporary administrative structures and could only be governed as a confederacy.
Historian David Bachrach notes the role of the bureaucracy and administration apparatus which the Ottonians inherited from the Carolingians and ultimately from the Ancient Romans, and which they developed greatly themselves: "It was the success of the Ottonians in molding the raw materials bequeathed to them into a formidable military machine that made possible the establishment of Germany as the preeminent kingdom in Europe from the tenth through the mid-thirteenth century.
