Frederick IV, (*11 October 1671 – †12 October 1730) was the king of Denmark and Norway from 1699 until his death. Frederick was the son of Christian V and Charlotte Amalie of Hesse-Kassel. For much of Frederik IV's reign Denmark was engaged in the Great Northern War (1700-1721) against Sweden. A first short-lived encounter 1700 ended with a Swedish invasion and threats from Europe's western naval powers. In 1709 Denmark again entered the war encouraged by the Swedish defeat at Poltava. Frederick IV commanded the Danish troops at the battle of Gadebusch in 1712. Although Denmark emerged on the victorious side, she failed to reconquer lost possessions in southern Sweden. The most important result was the destruction of the pro-Swedish duchy of Holstein-Gottorp re-establishing Denmark's domination in Schleswig-Holstein.
   His most important domestic reform was the abolition in 1702 of the so-called vornedskab, a kind of serfdom which had fallen on the peasants of Zealand in the later Middle Ages. His efforts were largely in vain because of the introduction of adscription in 1733. After the war, trade and culture flowered. The First Danish theatre, Lille Grönnegade was created and the great dramatist Ludvig Holberg began his career. Also the colonisation of Greenland was started by the missionary Hans Egede. Politically this period was marked by the king's connection to the Retentions, the Holsteiner relatives of his last queen, and by his growing suspicion toward the old nobility.
   During Frederick's rule Copenhagen was struck by two disasters: the plague of 1711, and the great fire of October 1728 which destroyed most of the medieval capital. Although the king had been persuaded by Ole Rømer to introduce the Gregorian calendar in Denmark-Norway in 1700, the astonomer's observations and calculations were among the treasures lost to the fire. Frederik IV, having twice visited Italy, had two pleasure palaces built in the Italian baroque style: Frederiksberg Palace and Fredensborg Palace, both considered monuments to the conclusion of the Great Northern War.
   Frederick was deemed a man of responsibility and industry — often regarded as the most intelligent of Denmark's absolute monarchs. He seems to have mastered the art of remaining independent of his ministers. Lacking all interest in academic knowledge, he was nevertheless a patron of culture, especially in art and architecture. His main weaknesses were probably pleasure-seeking and womanising (he is the only Danish king known to have committed bigamy), which sometimes distracted him.
   During King Frederick's last years he was afflicted with weak health and private sorrows that inclined him toward Pietism. That form of faith would rise to prevalence during the reign of his son. On his death in 1730, Frederick IV was interred in Roskilde Cathedral.