King of Sweden (1611–32). He was the grandson of Gustavus I and is generally recognized as Sweden’s greatest ruler. His partnership with the Chancellor, Oxenstierna, bore fruit in important reforms in the government, the armed forces, the economy, and education. His reign was notable for the absence of friction between crown and aristocracy.

Abroad he inherited three Baltic struggles: the Kalmar War with Denmark (1611–13); the Russian War (1611–17); and the intermittent conflict with Poland. The successes achieved by his mobile, highly motivated, and disciplined forces impressed Cardinal Richelieu, who negotiated the Treaty of Altmark (1629) between Sweden and Poland, so that the Swedes could be released for action in the Thirty Years War. Leaving the domestic government in the hands of Oxenstierna, Gustavus crossed to Germany in 1630 and proceeded to turn the tide of the war against the imperial forces. He was a devout Lutheran, and his war aims grew more ambitious as his invasion prospered. Originally intending to prevent the Catholic Habsburgs from dominating the Baltic, by 1632 he was pursuing grand imperial designs of his own. He was killed in action at Lützen.