Otto I, traditionally known as Otto the Great, was East Francian king from 936 and Holy Roman Emperor from 962 until his death in 973. He was the oldest son of Henry I the Fowler and Matilda.
Otto inherited the Duchy of Saxony and the kingship of the Germans upon his father's death in 936. 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 Roman Catholic 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 955, thus ending the Hungarian invasions of Western Europe. The victory against the pagan Magyars earned Otto a reputation as a savior of Christendom and secured his hold over the kingdom. By 961, Otto had conquered the Kingdom of Italy.