Landgrave William of Hesse-Cassel (1743-1821) was a German nobleman and a member of the House of Hesse. He ruled the Landgraviate of Hesse-Cassel from 1760 until his death, overseeing a period of economic development and military reform. William was known for his interest in agriculture and education, promoting advancements in these areas within his territory. William was also notable for his involvement in the Napoleonic Wars, where he initially sided with Napoleon Bonaparte but later shifted alliances. His reign was marked by efforts to modernize his state and improve the welfare of his subjects, leaving a lasting impact on Hesse-Cassel.