Duke Valdemar IV, also known as Valdemar the Victorious, was a notable figure in the history of Denmark. He ruled as Duke of Slesvig from 1340 until his death in 1375. Valdemar IV was known for his military campaigns and efforts to strengthen the duchy, as well as his attempts to expand his territory. His reign was marked by conflicts with neighboring regions, particularly Holstein and Schleswig. Valdemar IV's legacy includes his contributions to the political landscape of northern Europe during the late medieval period, as well as his role in the ongoing struggles for power among the various duchies and kingdoms of the time.