Frederick III was King of Denmark and Norway from 1648 until his death in 1670. He also governed under the name Frederick II as diocesan administrator of the Prince-Bishopric of Verden, and the Prince-Archbishopric of Bremen (1635–45).

The King's Law or Lex Regia was the absolutist constitution of Denmark and Norway from 1665 until 1849 and 1814, respectively. It established complete hereditary and absolute monarchy and formalized the king's absolute power, and is regarded the most sovereign form of all the European expressions of absolutism. Danish professor in legal history of the University of Copenhagen, Jens Chr. V. Johansen, asserts that with Europe's least circumscribed form of absolutism, Denmark "may be considered the most absolute of all the absolute European monarchies". It is the only formal constitution of any absolute monarchy, and has therefore been the subject of considerable historical and academic attention.