Miklos Horthy (18 June 1868 - 9 February 1957) styled "His Serene Highness the Regent of the Kingdom of Hungary," was an Austro-Hungarian naval officer who ascended to the position of Supreme Commander of the Austro-Hungarian fleet at the end of World War I. In 1919, following the collapse of the Dual Monarchy, he led the Hungarian National Army in its defeat of Communist revolutionary Bela Kun. In 1920, Horthy became Regent of the Kingdom of Hungary on behalf of the exiled Hapsburg king Charles IV, whom the Hungarian parliament blocked from the throne. After Charles' death in 1922, Horthy convinced Charles' son Otto von Hapsburg not to take the throne.
During World War II, Horthy brought Hungary into the war on the side of the Axis, but Adolf Hitler considered him an inadequately cooperative ally (he contributed little to the German war effort, and refused to deport Hungarian Jews). When Horthy opened up negotiations with the Allied Forces, Germany invaded Hungary in March 1944 and deposed Horthy that October, installing the Arrow Cross Party, which ruled for the duration of the war. Horthy was imprisoned in Germany until the end of the war, when he was liberated and immediately arrested by American forces. Horthy assisted the Allies in preparing evidence to be used in the upcoming war crimes tribunals against Nazi leadership, and testified against the Nazis' administrator of Hungary. In 1949, Horthy was allowed to emigrate to Portugal, where he lived out the rest of his life.
Initially, Miklos Horthy limited Hungary's involvement in the the Second World War seizing territorial claims against Czechoslovakia, making Hungary German's co-belligerent. Hungary also had territorial claims against Romania and Yugoslavia. However, while Britain and France had immediately severed ties with Hungary, neither made any military move against Hungary, nor did Hungary do much more than claim Czechoslovakian territory, a status quo that persisted into 1939. Horthy did use the commencement of hostilities in 1938 as an excuse to conscript a large army.
In late 1940, after the conclusion of the Hess Agreement, Horthy officially aligned with Germany and joined the war against the Soviet Union. Hungary remained a German ally even after the British and the French left their alliance before the end of 1941. Throughout the remainder of the war, Hungarian troops fought exclusively in the Ukraine. As a consequence of the historical animosity between Hungary and Germany's other staunch ally, Romania, the German military placed German units between the Hungarian and Romanian units on the lines. However, by 1943, Germany's situation was so dire that an unreliable ally was better than no ally.