Otto I of Austria (Sixtus Successful)

Otto I (Franz Joseph Otto Robert Maria Anton Karl Max Heinrich Sixtus Xavier Felix Renatus Ludwig Gaetan Pius Ignatius; 20 November 1912 - 4 July 2011) was Emperor of Austria, and King of Hungary (as Otto II, IV. Károly), King of Bohemia and a monarch belonging to the House of Habsburg-Lorraine. The eldest son of Charles I and IV, and his wife, Zita of Bourbon-Parma, Otto was born as third in line to the thrones, as Archduke Otto of Austria, Royal Prince of Hungary, Bohemia, and Croatia. With his father's accession to the thrones in 1916, he became Crown Prince of the Habsburg monarchy. Upon the early death of his father in 1922, Otto became Emperor at the age of 9. From 1 April 1922 to 20 November 1930, Otto's mother, Dowager Empress Zita, served as regent.

Otto ruled his country during its successful defense and victory over Nazi Germany during World War II, the revocation of the Ausgleich of 1867 which re-organized Austria-Hungary into the Empire of Austria, and the Cold War. He is considered by historians as one of the most influential figures of the 20th century and one of the most successful monarchs of modern history.

Otto died on 4 July 2011, after ruling his domains for almost 90 years as the longest-reigning monarch in modern history. He was succeeded by his son Charles.