The House of Habsburg ( /ˈhæps.bɜrɡ/; German pronunciation: [ˈhaːps.bʊʁk]), also Hapsburg, and also known as House of Austria is one of the most important royal houses of Europe and is best known for being an origin of all of the formally elected Holy Roman Emperors between 1438 and 1740, as well as rulers of the Austrian Empire and Spanish Empire and several other countries.

The House takes its name from Habsburg Castle, a fortress built around 1020–1030 AD in present day Switzerland by Count Radbot of Klettgau, who chose to name his fortress Habsburg. His grandson, Otto II, was the first to take the fortress name as his own, adding "von Habsburg" to his title. The House of Habsburg gathered dynastic momentum through the 11th, 12th and 13th centuries. By 1276, Count Radbot's seventh generation descendant, Rudolph of Habsburg, had moved the family's power base from Habsburg Castle to the Archduchy of Austria. Rudolph had become King of Germany/Holy Roman Emperor in 1273, but the dynasty of the House of Habsburg was truly entrenched in 1276 when Rudolph became sovereign ruler of Austria, which the Habsburgs ruled for the next six centuries.

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.

The 100: A Ranking of the Most Influential Persons in History is a 1978 book by Michael H. Hart, reprinted in 1992 with revisions. It is a ranking of the 100 people who, according to Hart, most influenced human history.

The first person on Hart's list is the Prophet of Islam Muhammad. Hart asserted that Muhammad was "supremely successful" in both the religious and secular realms. He also believed that Muhammad's role in the development of Islam was far more influential than Jesus' collaboration in the development of Christianity. He attributes the development of Christianity to St. Paul, who played a pivotal role in its dissemination."

The 1992 revisions included the demotion of figures associated with Communism, such as Vladimir Lenin and Mao Zedong, and the introduction of Mikhail Gorbachev. Hart took sides in the Shakespearean authorship issue and substituted Edward de Vere, 17th Earl of Oxford for William Shakespeare. Hart also substituted Niels Bohr and Henri Becquerel with Ernest Rutherford, thus correcting an error in the first edition. Henry Ford was also promoted from the "Honorary Mentions" list, replacing Pablo Picasso. Finally, some of the rankings were re-ordered, although no one listed in the top ten changed position.