Christian IV of Denmark

Christian IV took the throne of Denmark and Norway in 1588 at eleven, but didn't rule personally until 1596. For two decades he was the kind of king who initiates reforms, funds projects, and delivers stability rare in early modern Europe. Then came the Thirty Years' War. He entered in 1618 and stayed until his death in 1648, watching Germany burn and his own economy collapse under the cost. Conquered territories slipped away. He did rename Oslo after himself - Christiania held until 1925 - but the war hollowed out the wealth he'd built. He died in February 1648, the longest reign in Scandinavian history and a record of what ambition can build and then spend.