Frederick William III (German: Friedrich Wilhelm III) was king of Prussia from 1797 to 1840. He ruled Prussia during the difficult times of the Napoleonic Wars and the end of the Holy Roman Empire. Steering a careful course between France and her enemies, after a major military defeat in 1806, he eventually and reluctantly joined the coalition against Napoleon in the Befreiungskriege. Following Napoleon's defeat he was King of Prussia during the Congress of Vienna, which assembled to settle the political questions arising from the new, post-Napoleonic order in Europe. He was determined to unify the Protestant churches, to homogenize their liturgy, their organization and even their architecture. The long-term goal was to have fully centralized royal control of all the Protestant churches in the Prussian Union of churches.
Frederick William III died on 7 June 1840 in Berlin, survived by his second wife. His eldest son, Frederick William IV, succeeded him. Frederick William III is buried at the Mausoleum in Schlosspark Charlottenburg, Berlin.