The Duchy of Holstein was established by a Scandinavian monarch under what union?
Christian I of Denmark Christian I (February 1426 – 21 May 1481) was a Scandinavian monarch under the Kalmar Union. He was King of Denmark (1448–1481), Norway (1450–1481) and Sweden (1457–1464). From 1460 to 1481, he was also Duke of Schleswig (within Denmark) and Count (after 1474, Duke) of Holstein (within the Holy Roman Empire). He was the first Danish monarch of the House of Oldenburg.
Olaf II of Denmark Olaf II Haakonsson (1370 – 23 August 1387) was King of Denmark as Olaf II (1376–1387) and King of Norway as Olaf IV (1380–1387). Olaf was son of King Haakon VI of Norway and the grandson of King Magnus IV of Sweden. His mother was Queen Margaret I of Denmark which made him the grandson of King Valdemar IV of Denmark. In addition to his claim on the thrones of Denmark and later Norway, he was in the direct succession line to the throne of Sweden (but for the interposition of Albert of Mecklenburg).