Christian I of Denmark in the context of "Battle of Brunkeberg"

The House of Oldenburg is a German dynasty whose members rule or have ruled in Denmark, Iceland, Greece, Norway, Russia, Sweden, the United Kingdom, Livonia, Schleswig, Holstein, and Oldenburg. The current kings of Norway and the United Kingdom are patrilineal descendants of the Glücksburg branch of this house.

The dynasty rose to prominence when Count Christian I of Oldenburg was elected King of Denmark in 1448, of Norway in 1450 and of Sweden in 1457. Denmark's current monarch, King Frederik X, belongs to the Glücksburg branch of the House of Oldenburg through his mother, Queen Margrethe II.

The Duchy of Holstein (German: Herzogtum Holstein; Danish: Hertugdømmet Holsten) was the northernmost state of the Holy Roman Empire, located in the present German state of Schleswig-Holstein. It originated when King Christian I of Denmark had his County of Holstein-Rendsburg elevated to a duchy by Emperor Frederick III in 1474. Members of the Danish House of Oldenburg ruled Holstein – jointly with the Duchy of Schleswig – for its entire existence.

From 1490 to 1523 and again from 1544 to 1773 the Duchy was partitioned between various Oldenburg branches, most notably the dukes of Holstein-Glückstadt (identical with the Kings of Denmark) and Holstein-Gottorp. The duchy ceased to exist when the Kingdom of Prussia annexed it in 1866 after the Austro-Prussian War.

Karl Knutsson Bonde (c. 1408–1470), also known as Charles VIII and called Charles I in Norwegian contexts, was King of Sweden (1448–1457, 1464–1465 and 1467–1470) and King of Norway (1449–1450).

He rose in Swedish politics because Erik of Pomerania was unpopular and became regent after a rebellion by Engelbrekt Engelbrektsson. He held powerful posts, notably in Finland, where he acted semi-independently. After King Christopher's death in 1448, Karl was elected king of Sweden and briefly king of Norway (1449–1450), but was forced to relinquish the latter to Christian I of Denmark. His rule faced opposition from the nobility and church, especially amid war with Denmark from 1451. His consolidation of power alienated key factions like the Oxenstierna and Vasa families, leading to growing resistance that resulted in two rebellions, in 1457 and 1464.

Sten Sture the Elder (Swedish: Sten Sture den äldre; 1440 – 14 December 1503) was a Swedish statesman and regent of Sweden from 1470 to 1497 and again from 1501 to 1503. As the leader of the victorious Swedish separatist forces against the royal unionist forces led by Danish king Christian I during the Battle of Brunkeberg in 1471, he weakened the Kalmar Union considerably and became the effective ruler of Sweden as Lord Regent for most of his remaining life.

The Treaty of Ribe (Danish: Ribe-brevet meaning The Ribe letter; German: Vertrag von Ripen) was a proclamation at Ribe made in 1460 by King Christian I of Denmark to a number of Holsatian nobles enabling himself to become Count of Holstein and gain control of the Duchy of Schleswig, on Denmark's southern border. The most famous line of the proclamation was that the Danish Duchy of Schleswig and the County of Holstein within the Holy Roman Empire, should now be, in the original Middle Low German language, Up Ewig Ungedeelt, or "Forever Undivided".

Frederick I (Danish and Norwegian: Frederik; German: Friedrich; Swedish: Fredrik; 7 October 1471 – 10 April 1533) was King of Denmark and Norway from 1523 and 1524, respectively, until his death in 1533, and earlier co-duke Duke of Schleswig and Holstein.

A member of the House of Oldenburg, he was the youngest son of King Christian I and Dorothea of Brandenburg. Not originally destined for the throne, he received joint rule in Schleswig and Holstein on reaching his majority in 1490 and resided chiefly at Gottorf Castle.