The Landgrave of Hesse-Darmstadt was a title held by the rulers of the Hesse-Darmstadt territory in Germany. This region was part of the larger Landgraviate of Hesse, which was divided into several principalities. The Landgrave governed from the late 16th century until the early 19th century, overseeing local affairs and representing the territory in broader political matters. The title became less significant after the dissolution of the Holy Roman Empire in 1806, when Hesse-Darmstadt was elevated to a Grand Duchy. The last Landgrave, Louis IX, transitioned the title to Grand Duke, marking a shift in governance and status within the German states.