About Archduchess Elisabeth Marie of Austria
Archduchess Elisabeth Marie Henriette Stephanie Gisela of Austria was the only child of Rudolf, Crown Prince of Austria, and Princess Stéphanie of Belgium. Her father was the son and heir apparent of Emperor Franz Joseph I of Austria, and her mother was a daughter of King Leopold II of Belgium. She was known to her family as "Erzsi", a diminutive of her name Erzsébet in Hungarian. Later nicknamed The Red Archduchess, she was famous for becoming a socialist and a member of the Austrian Social Democratic Party. Franz Joseph resisted at first, having intended for Elisabeth to marry the German Crown Prince, but eventually relented. Otto did not descend from the first Prince of Windisch-Graetz, whose title as Prince of the Holy Roman Empire made his elder line of the Windisch-Graetz family legally equal for dynastic marriages with other royals.
Biography source: Wikipedia. The profile adds birthday-specific historical context from the Celebs Birthday Today editorial database.