Reichsdeputationshauptschluss
Following the reorganization of the German states during the German mediatization of 1803, the Landgraviate of Hesse-Kassel was raised to the Electorate of Hesse and Landgrave William IX was elevated to Imperial Elector, taking the title William I, Elector of Hesse. The principality thus became known as "", although it is still usually referred to as Hesse-Kassel.