Christian IV (; 12 April 1577 – 28 February 1648), sometimes colloquially referred to as Christian Firtal in Denmark and Christian Kvart or Quart in Norway, was a monarch of the German House of Oldenburg who ruled as king of Denmark-Norway from 1588 to 1648. His reign of 59 years is the longest of all Danish monarchs, and the longest of all the Scandinavian monarchies.