The Holy Roman Emperor, originally and officially the Emperor of the Romans (Latin: Imperator Romanorum, German: Kaiser der Rmer) during the Middle Ages, and also known as the German-Roman Emperor since the early modern period (Latin: Imperator Germanorum, German: Rmisch-deutscher Kaiser, lit.'Roman-German emperor'), was the ruler and head of state of the Holy Roman Empire. The empire was considered by the Roman Catholic Church to be the only successor of the Roman Empire during the Middle Ages and the early modern period. The title was held in conjunction with the title of king of Italy (Rex Italiae) from the 8th to the 16th century, and, almost without interruption, with the title of king of Germany (Rex Teutonicorum, lit. King of the Teutons) throughout the 12th to 18th centuries.In theory and diplomacy, the emperors were considered primus inter pares, regarded as first among equals among other Roman Catholic monarchs across Europe.From an autocracy in Carolingian times (AD 800924) the title by the 13th century evolved into an elective monarchy, with the emperor chosen by the prince-electors.

Various royal houses of Europe, at different times, became de facto hereditary holders of the title, notably the Ottonians (9621024) and the Salians (10271125). Following the late medieval crisis of government, the Habsburgs kept possession of the title without interruption from 1440 to 1740. The final emperors were from the House of Habsburg-Lorraine, from 1765 to 1806. The Holy Roman Empire was dissolved by Francis II, after a devastating defeat by Napoleon at the Battle of Austerlitz.

The emperor was widely perceived to rule by divine right, though he often contradicted or rivaled the pope, most notably during the Investiture controversy. The Holy Roman Empire never had an empress regnant, though women such as Theophanu and Maria Theresa exerted strong influence. Throughout its history, the position was viewed as a defender of the Roman Catholic faith. Until Maximilian I in 1508, the emperor-elect (Imperator electus) was required to be crowned by the pope before assuming the imperial title. Charles V was the last to be crowned by the pope in 1530. Even after the Reformation, the elected emperor was always a Roman Catholic. There were short periods in history when the electoral college was dominated by Protestants, and the electors usually voted in their own political interest.

Leopold I (Leopold Ignaz Joseph Balthasar Felician; Hungarian: I. Lipót; 9 June 1640 – 5 May 1705) was Holy Roman Emperor, King of Hungary, Croatia, and Bohemia. The second son of Ferdinand III, Holy Roman Emperor, by his first wife, Maria Anna of Spain, Leopold became heir apparent in 1654 by the death of his elder brother Ferdinand IV. Elected in 1658, Leopold ruled the Holy Roman Empire until his death in 1705, becoming the longest-ruling Habsburg emperor (46 years and 9 months). He was both a composer and considerable patron of music.

Leopold's reign is known for conflicts with the Ottoman Empire in the Great Turkish War (1683-1699) and rivalry with Louis XIV, a contemporary and first cousin (on the maternal side; fourth cousin on the paternal side), in the west. After more than a decade of warfare, Leopold emerged victorious in the east thanks to the military talents of Prince Eugene of Savoy. By the Treaty of Karlowitz, Leopold recovered almost all of the Kingdom of Hungary, which had fallen under Turkish power in the years after the 1526 Battle of Mohács.

Leopold fought three wars against France: the Franco-Dutch War, the Nine Years' War, and the War of the Spanish Succession. In this last, Leopold sought to give his younger son Charles the entire Spanish inheritance, disregarding the will of the late Charles II. Leopold started a war that soon engulfed much of Europe. The early years of the war went fairly well for Austria, with victories at Schellenberg and Blenheim, but the war would drag on until 1714, nine years after Leopold's death, which barely had an effect on the warring nations. When peace returned with the Treaty of Rastatt, Austria could not be said to have emerged as triumphant as it had from the war against the Turks.