The Landgraves of Hesse were rulers of the historical region of Hesse in central Germany. This title originated in the 13th century and was held by various noble families, most notably the House of Hesse. The Landgraves played a significant role in the political and cultural development of the region, particularly during the Holy Roman Empire. The most famous Landgrave was Philip I of Hesse, known for his support of the Reformation and his alliance with Martin Luther. The Landgraves ruled until the 19th century, when the title was replaced by the Grand Duchy of Hesse, reflecting changes in European governance and the rise of nation-states.