Valdemar IV of Denmark (1320-24 October 1375) was King of Denmark from 2 August 1332 to 24 October 1375, succeeding Christopher II and preceding Olaf II. He ended Denmark's "Age of Decay" by reconquering Denmark from the German nobles of Holstein and Gotaland from Sweden, and he also replenished the treasury by selling Danish Estonia to the Teutonic Order in 1346.
Valdemar was the youngest son of King Christopher II of Denmark and Euphemia of Pomerania, and he spent his childhood and youth in exile in Bavaria. From 1332 to 1340, Denmark was thrown into anarchy during a long interregnum, and Valdemar came to the throne following Gerhard III of Holstein-Rendsburg's murder in 1340. He married the daughter of Eric II of Schleswig (the sister of Valdemar III of Denmark) and came to control a quarter of Jutland, and he then fought against the Holsteiners to conquer the rest of Jutland from them. He became the first Danish king to reign from Copenhagen, reclaiming Denmark through military force or paying off his family's debts. He sold Danish Estonia to the Teutonic Order in 1346 and led a crusade against Lithuania that same year, but he ultimately travelled to Jerusalem and abandoned his crusade. In 1346, he reconquered Zealand from Holstein, and, by 1347, he had thrown the Germans out of Denmark and reunited the country. The outbreak of the Black Plague in 1349 delayed Valdemar's invasion of Scania in southern Sweden, and he resumed his campaign against Holstein in the 1350s. In 1360, he reconquered Helsingborg and Scania from Magnus IV of Sweden, and he also captured Halland and Blekinge. In 1361, he conquered Gotland at the Battle of Visby, but his action against Gotland led to a rivalry with the Hanseatic League. He fell ill in 1375 while campaigning in southern Jutland and died in October.