Frederick Augustus I, 1750–1827, king (1806–27) and elector (1763–1806) of Saxony, grand duke of Warsaw (1807–14). He sided with the allies in the French Revolutionary Wars and joined Prussia in the campaign of 1806 against the French emperor Napoleon I. However, after the French victory at Jena he made a separate peace with Napoleon, with whose approval he took the title king of Saxony. Napoleon also made him nominal ruler of the grand duchy of Warsaw. Frederick Augustus did not abandon his alliance with Napoleon in time and as a result lost a large part of Saxony to Prussia at the Congress of Vienna (1815).

Frederick Augustus I, elector of Saxony: see Augustus II, king of Poland.