Landgrave William IX of Hesse (1743-1821) was a German nobleman and a member of the House of Hesse. He ruled the Landgraviate of Hesse-Kassel from 1783 until his death. William IX is known for his efforts to modernize his territory, promoting economic development and education. In addition to his political role, William IX was a patron of the arts and sciences. He supported various cultural initiatives and was involved in the establishment of institutions that contributed to the intellectual life of his region, reflecting the broader trends of the Enlightenment during his time.