Alexander I Aldea (1431–1436) was the first Romanian ruler to be forced to render military service to the Ottomans. Two decades later, Vlad III the Impaler (1448, 1456–1462, 1476), notorious as the model for the Dracula legend, turned against the Ottoman Empire. He carried out a series of attacks across the Danube in the winter of 1461–1462. The response was a massive invasion led by Mehmed II who drove Vlad III from the throne and replaced him with his brother, Radu III the Fair (1462–1475). Due to the frequent military operations, the Wallachian Plain was heavily depopulated after the end of the 14th century. On the other hand, Wallachia received a steady flow of immigrants, mostly from the Balkans.