The Habsburg Monarchy (or Habsburg Empire) covered the territories ruled by the junior Austrian branch of the House of Habsburg (1278–1780), and then by the successor House of Habsburg-Lorraine (from 1780), between 1526 and 1867/1918. The Imperial capital was Vienna, except from 1583 to 1611, when it was moved to Prague. From 1804 to 1867 the Habsburgs ruled the Austrian Empire and from 1867 to 1918 Austria-Hungary.

The head of the House of Habsburg was usually also the ruler of the Holy Roman Empire from 1440 until its dissolution in 1806. However, the two entities should not be considered coterminous, as the Habsburg Empire covered many lands beyond the Holy Roman Empire, and not all of the Holy Roman Empire was de facto under direct Habsburg control at any given time. In some contexts, the term "Habsburg Empire" might also refer to extended Habsburg family possessions once ruled solely by Charles V, Holy Roman Emperor, or to the Spanish Empire ruled by the senior Spanish branch of the house.

Frederick II (German: Friedrich II.; 24 January 1712 – 17 August 1786) was a King in Prussia (1740–1772) and a King of Prussia (1772–1786) from the Hohenzollern dynasty. In his role as a prince-elector of the Holy Roman Empire, he was also Elector of Brandenburg. He was in personal union the sovereign prince of the Principality of Neuchâtel. He became known as Frederick the Great (Friedrich der Große) and was named Der Alte Fritz ("Old Fritz").

Interested primarily in music and philosophy and not the arts of war during his youth, Frederick unsuccessfully attempted to flee from his authoritarian father, Frederick William I, with childhood friend Hans Hermann von Katte, whose execution he was forced to watch after they were captured. Upon ascending to the Prussian throne, he attacked Austria and claimed Silesia during the Silesian Wars, winning military acclaim for himself and Prussia. Near the end of his life, Frederick physically connected most of his realm by conquering Polish territories in the First Partition of Poland.

Otto von Habsburg (20 November 1912 – 4 July 2011), also known by his royal name as Archduke Otto of Austria, was the last Crown Prince of Austria-Hungary from 1916 until the dissolution of the empire in 1918, a realm which comprised modern-day Austria, Hungary, Bosnia and Herzegovina, Croatia, the Czech Republic, Slovakia, Slovenia, and parts of Italy, Montenegro, Poland, Romania, Serbia and Ukraine. He remained the Crown Prince of Hungary until also the deposition of the Habsburgs in Hungary in 1921. He subsequently became the pretender to the former thrones, Head of the Imperial House of Habsburg, and Sovereign of the Order of the Golden Fleece in 1922. He resigned as Sovereign of the Golden Fleece in 2000 and as head of the Imperial House in 2007.

The eldest son of Charles I, the last Emperor of Austria and King of Hungary, and his wife, Zita of Bourbon-Parma, Otto was born as third in line to the thrones, as His Imperial and Royal Highness Archduke and Prince Imperial Otto of Austria, Prince Royal of Hungary, Croatia and Bohemia. With his father's accession to the thrones in 1916, he was himself likely to become the Emperor. As his father never abdicated, Otto was considered by himself, his family and Austro-Hungarian legitimists to be the rightful Emperor-King from 1922.