The Duke of Guelders was a title held by the rulers of the historical region of Guelders, located in what is now the eastern part of Netherlands and western Germany. The duchy played a significant role in the politics of medieval Europe, often involved in conflicts with neighboring territories and dynasties. The title was established in the 15th century and became prominent under the rule of Duke Charles of Guelders. The duchy was known for its rich culture and strategic importance, eventually becoming part of the Habsburg territories in the 16th century after a series of conflicts and dynastic marriages.