Otto von Habsburg, also known as Archduke Otto of Austria, should have succeeded his father at the throne, but had to go into exile after the collapse of the Austro-Hungarian Empire in 1919. A fervent Austrian patriot, Otto von Habsburg opposed the Nazi Anschluss in Austria in 1938. He returned to Austria in 1966 after 48 years in exile, renouncing all claims to the Austrian throne.

He was honorary president of the International Paneuropean Union and a former member of the European Parliament for the Christian Social Union of Bavaria (CSU).

Otto von Habsburg, who lived in Poecking in Lower Bavaria, in the last years, also held Croatian citizenship and was a staunch advocate for Croatia's admission to the European Union. Being a polyglot, he spoke Croatian, too.

He visited Croatia often, using those occasions to highlight that this country belonged to Europe.

"When you are in Varazdin, it seems to you as if you are in Austria. If you are in Dubrovnik, as if you are in Venice," he said in 2004.

Otto von Habsburg, also known as Archduke Otto of Austria, offered big assistance to Croatia during the Homeland Defence War and believed in the country's economic revival modelled on post-war Germany.

Lobbying for Croatia's EU road, this Archduke countered the claims by a former chief prosecutor of the UN tribunal in The Hague (ICTY), Carla del Ponte, about Croatia's cooperation with the tribunal. He criticised her for the approach that indicted people should prove their innocence which he said was a wrong legal principle.

European Commission President Jose Manuel Barroso has said that Otto von Habsburg gave a central contribution to the opening of the Iron Curtain between the East and the West.

A message which Barroso gave on the passing of Otto von Habsburg reads that "With Otto von Habsburg, a great European has left us who gave an important impetus to the European project throughout his rich life. As a long-serving member of the European Parliament and its Doyen he marked the European success story. In his capacity as the President of the International Paneuropean Union he made a central contribution to the opening of the iron curtain and the peaceful reunification of our continent that had been divided for too long."

Barroso said that he would "particularly remember his strong stance against all forms of totalitarianism and on Europe's fundamental values. Otto von Habsburg's commitment to Europe should set a political example for all of us, especially in difficult times."

The head of the European People's Party (EPP Group) in the European Parliament, Joseph Daul, described Otto von Habsburg as a man who had struggled all his life for democracy, freedom and better understanding among peoples.