It is strange how a descent, no matter how tenuous, can at times become important. William The Conqueror chose Matilda of Flanders as wife with her descent from Alfred The Great of England in mind. The link of Christian I to previous kings of Denmark was much more remote than those of Matilda to the Wessex kings of England.
When King Christopher III of Denmark, Norway and Sweden died childless, Duke Adolf VIII von Schleswig was at first approached to be the new king. However, he declined and suggested his sister's son, who after all was a descendant of King Eric Klipping.
The nephew agreed and, after being elected, this Count von Oldenburg was crowned and became Christian I, King of Denmark, Norway and Sweden. He married his predecessor's young widow, Dorothea von Brandenburg. The decision of the Danish and Swedish councils, which recognised him as king of Norway and heir in Sweden, was disputed by the Swedish King Charles VIII. This resulted in a war between Denmark and Sweden which lasted from 1451 until 1457. After King Charles VIII
was deposed, Christian I held Sweden until 1464 when he was overthrown by part of the Swedish nobility. In 1465 he regained Sweden, this time only until 1467. In 1471 he made his last full-scale attempt to gain sovereignty over Sweden but was defeated by Sten Sture the Elder in a battle at Brunkeberg near Stockholm.
Son and heir of the Count von Oldenburg and Delmenhorst, he gave these to his brother; but Schleswig and Holstein, inherited in 1460 from the same Duke Adolf VIII, became part of Denmark for several
hundreds of years. Financially weak because of the Swedish wars, he became dependant upon the Hanseatic League, a trading confederation of North German cities, and was forced to give them generous commercial privileges. When the Hanseatic traders challenged English trading rights in Iceland, he was drawn into a war with England.In 1469 his daughter, Margaret, married James III, King of Scotland and the Norwegian controlled Orkney and Shetland islands were mortgaged to Scotland to help pay for Margaret's dowry; as well, the annual rent paid by Scotland for the Hebrides Islands and the Isle of Man were cancelled.
Christian I concluded a concordat with Pope Sixtus IV, improving his relations with the Danish Church. He is the founder of the Order of the Elephant. In 1474 he visited Rome and obtained a papal bull for
a university, which was founded in Copenhagen. Here he died after a reign of almost thirty-three years, 21 May 1481, aged 55.
 

Source: Leo van de Pas