Frederick I of Denmark and Norway (October 1 1471 – April 10 1533) was the son of King Christian I Oldenbourg of Denmark, Norway and Sweden (1426-1481) and of Dorothea of Brandenburg (1430-1495). The name is also spelled Friedrich in German, Frederik in Danish, and Fredrik in Swedish.

Frederick was elected co-Duke of Schleswig and Holstein in 1482, after the death of his father, the other co-duke being his ten years younger brother Johann (or Hans). At Frederick's majority in 1490 both duchies were divided between the brothers. In 1500 he'd convinced his brother and co-duke for a conquest of Dithmarschen, and a great army was called from not only the duchies, but with additions from all of the Kalmar Union for which his brother briefly was king. Also numerous German mercenaries took part. The expedition failed however miserably in the Battle of Hemmingstedt, where one third of all knights of Schleswig and Holstein lost their lives.

In 1502 he married Anna of Brandenburg (15 years old; a daughter of the cousin of his mother; 1487-1514). The couple had two children: Christian III (born in 1503) and Dorothea (born in 1504).

Frederick's wife Anna died on May 5 1514, 26 years old.

Four years later, Frederick married Sophie of Pomerania (20 years old; 1498-1568), a daughter of Duke Bogislaw "the Great" of Pomerania. Sophie and Frederic had six children: Duke Johan of Holstein ( born in 1521), Elisabeth (born in 1524), Duke Adolf of Holstein (born in 1526), Anna, Dorothea (dead 1528) and Bishop Friedrich of Hildesheim and Schleswig (born in 1532).

In 1523 his nephew, the King of Denmark and Sweden, was forced to abdicate. So he became the new King as Frederick I.

In 1525 his son, the following king Christian, married Dorothea of Saxe-Lauenburg (14 years old; 1511-1571).

He died on April 10 1533 in Gottorp. He was 61.