Waldemar IV (Valdemar Atterdag), c.1320–1375, king of Denmark (1340–75). He became king of a land completely dismembered by foreign rulers, but his ambition, unscrupulousness, and military ability enabled him to unite his kingdom by 1361. Waldemar IV married his daughter Margaret I to Haakon VI, king of Norway, in an effort to unite Denmark and Norway. He interfered in Germany on behalf of his kinsman, the margrave of Brandenburg. His conquest of Skane, in violation of a treaty with the Swedish king, gave him control of the lucrative fishing industry, and his defeat (1362) of the Hanseatic League secured him temporary possession of Gotland. In 1368, however, the Hanseatic towns, Mecklenburg, Sweden, and Holstein formed a coalition against him. Defeated, Waldemar was forced to consent (1370) to the humiliating Treaty of Stralsund, which granted freedom of trade in Denmark to the Hanseatic League. He was succeeded by Margaret's son, Olaf, under his parents' regency.
See F. Pratt, The Third King (1950).