Christian IV (12 April 1577 – 28 February 1648) was King of Denmark and Norway and Duke of Holstein and Schleswig from 1588 until his death in 1648. His reign of 59 years and 330 days is the longest in Scandinavian history. A member of the House of Oldenburg, Christian began his personal rule of Denmark-Norway in 1596 at the age of 19. He is remembered as one of the most popular, ambitious, and proactive Danish-Norwegian kings, having initiated many reforms and projects. Christian IV obtained for his kingdoms a level of stability and wealth that was virtually unmatched elsewhere in Europe. He engaged Denmark-Norway in numerous wars, most notably the Thirty Years' War (1618–1648), which devastated much of Germany, undermined the Danish economy, and cost Denmark-Norway some of its conquered territories. He rebuilt and renamed the Norwegian capital Oslo as Christiania after himself, a name used until 1925. Source: Wikipedia (en)