Wenceslaus I of Bohemia
In 1251, Ottokar's father King Wenceslaus I of Bohemia had not only granted him the title of a Margrave of Moravia, but also installed him as duke of Austria and Styria, territories that were princeless after the ruling Babenberg dynasty had become extinct in 1246. To legitimate his succession, Ottokar in 1252 married the Duchess Margaret of Austria, the sister of the last Babenberg duke and about 26 years his senior.