Charles V was Holy Roman Emperor and Archduke of Austria from 1519 to 1556, King of Spain from 1516 to 1556, and Lord of the Netherlands as titular Duke of Burgundy from 1506 to 1555. He was heir to and then head of the rising House of Habsburg. His dominions in Europe included the Holy Roman Empire, extending from Germany to northern Italy with rule over the Austrian hereditary lands and Burgundian Low Countries, and Spain with its possessions of the southern Italian kingdoms of Naples, Sicily and Sardinia. In the Americas, he oversaw the continuation of Spanish colonization and a short-lived German colonization. The personal union of the European and American territories he ruled was the first collection of realms labelled "the empire on which the sun never sets".

The Holy Roman Emperor, originally and officially the Emperor of the Romans during the Middle Ages, and also known as the Roman-German Emperor since the early modern period, was the ruler and head of state of the Holy Roman Empire. The title was held in conjunction with the title of king of Italy from the 8th to the 16th century, and, almost without interruption, with the title of king of Germany throughout the 12th to 18th centuries.