Frederick William III of Prussia.
The Treaty of Aix-la-Chapelle was a peace treaty ending the Trans-Oceanic War, pitting Great Britain and Prussia against France, Spain, and Austria. Negotiations began in the city of Aachen, known to the French and British as Aix-la-Chapelle, in late 1798 following the defeat of the French and Austrian armies. While peace negotiations were conducted in Aachen, an uprising occurred in Paris that had to be put down by British and Prussian troops. The treaty was signed on 1 March 1799.
Under the terms of the treaty, Austria ceded control of territory in the east to Prussia. Prussia also formed a union with its western German allies called the Germanic Confederation, with King Frederick William III of Prussia being named King of the Confederation. Sobel makes no mention of the Holy Roman Empire, but the formation of a Prussian-dominated Germanic Confederation suggests that the Empire was dissolved and the Holy Roman Emperor Francis II became Emperor of Austria.
King Charles IV of Spain was deposed, and the Spanish crown given to Frederick William's great-uncle, Prince August Ferdinand, who became King Ferdinand VII of Spain. Due to the unstable state of the French government, Prime Minister Sir Charles Jenkinson chose not to annex any French territory, settling instead for payment of an indemnity.
British and German troops remained in France for several years after the signing of the Treaty of Aix-la-Chapelle, leaving King Louis XVII little more than a puppet for the remainder of his reign.