St. Stephen's Cathedral (German: Stephansdom) is the mother church of the Archdiocese of Vienna and the seat of the Archbishop of Vienna, Christoph Cardinal Schönborn, OP. Its current Romanesque and Gothic form seen today, situated at the heart of Vienna, Austria in the Stephansplatz, was largely initiated by Rudolf IV and stands on the ruins of two earlier churches, the first being a parish church consecrated in 1147. As the most important religious building in Austria's capital, the cathedral has borne witness to many important events in that nation's history and has, with its multi-colored tile roof, become one of the city's most recognizable symbols.

By the middle of the 12th century, Vienna had become an important centre of German civilization in eastern Europe, and the four existing churches, including only one parish church, no longer met the town's religious needs. In 1137, Bishop of Passau Reginmar and Margrave Leopold IV signed the Treaty of Mautern, which referred to Vienna as a Civitas for the first time and transferred the Church of St. Peter to the Diocese of Passau. Under the Treaty, Margrave Leopold IV also received from the Bishop extended stretches of land beyond the city walls, with the notable exception of the territory allocated for the new parish church which would eventually become St. Stephen's Cathedral. Although previously believed to have been built in an open field outside the city walls, the new parish church was in actuality likely built on an ancient cemetery dating back to Ancient Roman times; excavations for a heating system in 2000 revealed graves, 2.5 meters below the surface, which were carbon-dated to the 4th century.^{[citation needed]} This discovery suggests that an even older religious building predated the Ruprechtskirche, which is considered today to be the oldest church in Vienna.

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.