Holy Roman Empire
Since Charlemagne, the polity was simply called the Roman Empire. The name "Holy Roman Empire" was not used until the 13th century. Before that time, people called the empire by different names like universum regnum ("the whole kingdom", meaning it included all regions, not just local kingdoms), and imperium christianum ("Christian empire"). The emperor's right to rule came from the idea of translatio imperii ("transfer of rule") meaning that he had the highest power passed down from the Ancient Roman emperors.