Known by his royal name as Archduke Otto of Austria, he 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 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, upon the death of his father. 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 and IV, 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.
Otto was active on the Austrian and European political stage from the 1930s, both by promoting the cause of Habsburg restoration and as an early proponent of European integration—being thoroughly disgusted with nationalism—and a fierce opponent of Nazism and communism. He has been described as one of the leaders of the Austrian anti-Nazi resistance. After the 1938 Anschluss, monarchists were severely persecuted in Austria, and—sentenced to death by the Nazis—Otto fled to the United States, with a visa issued by Aristides de Sousa Mendes.
Otto von Habsburg was Vice President (1957–1973) and President (1973–2004) of the International Paneuropean Union, and served as a Member of the European Parliament for the Christian Social Union of Bavaria (CSU) 1979–1999. As a newly elected Member of the European Parliament in 1979, Otto had an empty chair set up for the countries on the other side of the Iron Curtain in the European Parliament, and took a strong interest in the countries behind the Iron Curtain during his tenure. Otto von Habsburg played a central role in the revolutions of 1989, as a co-initiator of the Pan-European Picnic. Later he would be a strong supporter of the EU membership of central and eastern European countries. A noted intellectual, he has published several books on historical and political affairs. Otto has been described as one of the “architects of the European idea and of European integration” together with Robert Schuman, Konrad Adenauer, and Alcide De Gasperi.
Otto was exiled in 1918 and grew up mostly in Spain. His devout Catholic mother raised him according to the old curriculum of Austria-Hungary, preparing him to become a Catholic monarch. During his life in exile, he lived in Switzerland, Madeira, Spain, Belgium, France, the United States, and from 1954 until his death, finally in Bavaria (Germany), in the residence Villa Austria.
He died 4 July 2011.

Link to Wikipedia biography