Gustavus Adolphus (9 December [N.S 19 December] 1594 – 6 November [N.S 16 November] 1632), also known in English as Gustav II Adolf or Gustav II Adolph, was King of Sweden from 1611 to 1632, and is credited for the rise of Sweden as a great European power (Swedish: Stormaktstiden). During his reign, Sweden became one of the primary military forces in Europe during the Thirty Years' War, helping to determine the political and religious balance of power in Europe. He was formally and posthumously given the name Gustavus Adolphus the Great (Swedish: Gustav Adolf den store; Latin: Gustavus Adolphus Magnus) by the Riksdag of the Estates in 1634.
He is often regarded as one of the greatest military commanders in modern history, with use of an early form of combined arms. His most notable military victory was the Battle of Breitenfeld (1631). With his resources, logistics, and support, Gustavus Adolphus was positioned to become a major European leader, but he was killed a year later at the Battle of Lützen (1632). He was assisted in his efforts by Count Axel Oxenstierna, the Lord High Chancellor of Sweden, who also acted as regent after his death.
Coming to the throne at the age of 16, Gustavus Adolphus inherited three wars from his father Charles IX of Sweden; border conflicts with Russia and Denmark-Norway, and a dynastic struggle with his first cousin, King Sigismund III Vasa of Poland. Of these, the Danish war was the most serious. During his reign, Sweden rose from the status of a Baltic Sea basin regional power to one of the great powers of Europe and a model of early modern era government. Gustavus Adolphus is known as the "father of modern warfare", or the first modern general. He taught a number of other military commanders, such as Lennart Torstensson, who would go on to expand the boundaries and the power of Swedish Empire after Gustavus Adolphus's death. Spoils meant he became a successful bookraider in Europe, targeting Jesuit collections.
His contributions to Sweden's rise in power included reformation of the administrative structure. For example, he began parish registration of the population, so that the central government could more efficiently tax and conscript the people.
He is widely commemorated by Protestants in Europe as the main defender of their cause during the Thirty Years' War, with multiple churches, foundations and other undertakings named after him, including the Gustav-Adolf-Werk.