The original design of the Netherlands as a kingdom can be attributed to King William I of the Netherlands. He was the first King of the Netherlands, reigning from 1815 to 1840. King William I played a crucial role in establishing the modern state of the Netherlands after the fall of Napoleon, and he was instrumental in the formation of the United Kingdom of the Netherlands, which initially included present-day Belgium and Luxembourg. His reign marked the beginning of the constitutional monarchy in the Netherlands.