Otto I, Holy Roman Emperor engaged in war.
Leopold I, Holy Roman Emperor . To this end , he started a war which soon engulfed much of Europe . Otto I ( 23 November 912 -- 7 May 973 ) , traditionally known as Otto I the Great ( Otto I. der Große ) , was German king from 936 and emperor of the Holy Roman Empire from 962 until his death in 973 . 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 .