Magnus of Denmark or Magnus of Holstein was a Prince of Denmark, Duke of Holstein, and a member of the House of Oldenburg. As a vassal of Tsar Ivan IV of Russia, he was the titular King of Livonia from 1570 to 1578.

The House of Oldenburg is an ancient dynasty of German origin whose members rule or have ruled in Denmark, Iceland, Greece, Norway, Russia, Sweden, the United Kingdom, Livonia, Schleswig, Holstein, and Oldenburg. The current King of the United Kingdom and King of Norway are agnatic members of this house, meanwhile the King of Spain and King of Denmark are matrilineal members.