The Holy Roman Emperor was the ruler of the Holy Roman Empire. From an autocracy in Carolingian times the title evolved into an elected monarchy chosen by the Prince-electors, until the Reformation the Emperor elect was required to be crowned by the Pope before assuming the imperial title. The title was held in conjunction with the rule of the Kingdom of Germany, in theory, the Holy Roman Emperor was primus inter pares among the other Catholic monarchs, in practice, a Holy Roman Emperor was only as strong as his army and alliances made him. Various royal houses of Europe, at different times, effectively became hereditary holders of the title, after the Reformation many of the subject states and most of those in Germany were Protestant while the Emperor continued to be Catholic. The Holy Roman Empire was dissolved by the last Emperor as a result of the collapse of the polity during the Napoleonic wars, from the time of Constantine I the Roman emperors had, with very few exceptions, taken on a role as promoters and defenders of Christianity. In the west, the title of Emperor was revived in 800, as the power of the papacy grew during the Middle Ages, popes and emperors came into conflict over church administration. The best-known and most bitter conflict was known as the Investiture Controversy. After Charlemagne was crowned Emperor of the Romans by Pope Leo III, no pope appointed an emperor again until the coronation of Otto the Great in 962. Under Otto and his successors, much of the former Carolingian kingdom of Eastern Francia fell within the boundaries of the Holy Roman Empire, the various German princes elected one of their peers as King of the Germans, after which he would be crowned as emperor by the Pope. After Charles Vs coronation, all succeeding emperors were called elected Emperor due to the lack of papal coronation, the term sacrum in connection with the medieval Roman Empire was first used in 1157 under Frederick I Barbarossa. Charles V was the last Holy Roman Emperor to be crowned by the Pope, the final Holy Roman Emperor-elect, Francis II, abdicated in 1806 during the Napoleonic Wars that saw the Empires final dissolution. The standard designation of the Holy Roman Emperor was August Emperor of the Romans, the word Holy had never been used as part of that title in official documents. In German-language historiography, the term Römisch-deutscher Kaiser is used to distinguish the title from that of Roman Emperor on one hand, the English term Holy Roman Emperor is a modern shorthand for emperor of the Holy Roman Empire not corresponding to the historical style or title. Successions to the kingship were controlled by a variety of complicated factors, elections meant the kingship of Germany was only partially hereditary, unlike the kingship of France, although sovereignty frequently remained in a dynasty until there were no more male successors. The Electoral council was set at seven princes by the Golden Bull of 1356, another elector was added in 1690, and the whole college was reshuffled in 1803, a mere three years before the dissolution of the Empire. After 1438, the Kings remained in the house of Habsburg and Habsburg-Lorraine, with the exception of Charles VII. Maximilian I and his successors no longer travelled to Rome to be crowned as Emperor by the Pope, Maximilian therefore named himself Elected Roman Emperor in 1508 with papal approval. This title was in use by all his uncrowned successors, of his successors only Charles V, the immediate one, received a papal coronation
Coats of arms of prince electors surround the Holy Roman Emperor's; from flags book of Jacob Köbel (1545). Electors voted in an Imperial Diet for a new Holy Roman Emperor.
Illustration of the election of Henry VII (27 November 1308) showing (left to right) the Archbishop of Cologne, Archbishop of Mainz, Archbishop of Trier, Count Palatine of the Rhine, Duke of Saxony, Margrave of Brandenburg and King of Bohemia (1341 miniature).