A full bio can be found here – it is in German though! He was an important member of the Hungarian branch of the Austro-Hungarian royal family of Habsburg -Lotharingen.
Born in 1872 in Hungary he had a military career spanning form lieutenant in 1890 up to full Field Marshall and the royal representative for Hungary in 1918.
The collecting of autographs is not a new trend but already existed in the late 19th and early 20th century and even before. This autograph was send to a Austrian collector, Fritz Wölfler, of autographs op public people of the Austro-Hungarian empire in the early 20th century. The collection was sold by a dealer in 2007 on Ebay in Austria.
It seems to be a short version of his autograph. The full version can be seen below (photo taken from Facebook – not my collection).