Early modern period
In the early modern period, the Holy Roman Empire was a union of territories in Central Europe under a Holy Roman Emperor the first of which was Otto I. The last was Francis II, who abdicated and dissolved the Empire in 1806 during the Napoleonic Wars. Despite its name, for much of its history the Empire did not include Rome within its borders.
Holy Roman Emperor
After the coronation of Charlemagne, his successors maintained the title until the death of Berengar I of Italy in 924. The comparatively brief interregnum between 924 and the coronation 
of Otto the Great in 962 is taken as marking the transition from the Frankish Empire to the Holy Roman Empire.
Under the Ottonians, much of the former Carolingian kingdom of Eastern Francia fell within the boundaries of the Holy Roman Empire.