WordNet sense 1 (the last king of Sweden to have any real political power (1882-1973)):

Gustavus VI

WordNet sense 2 (king of Sweden who kept Sweden neutral during both World War I and II (1858-1950)):

Gustavus V

WordNet sense 3 (king of Sweden whose losses to Napoleon I led to his being deposed in 1809 (1778-1837)):

Gustavus IV

WordNet sense 4 (king of Sweden who increased the royal power and waged an unpopular war against Russia (1746-1792)):

Gustavus III

WordNet sense 5 (king of Sweden whose victories in battle made Sweden a European power; his domestic reforms made Sweden a modern state; in 1630 he intervened on the Protestant side of the Thirty Years' War and was killed in the battle of Lutzen (1594-1632)):

Gustavus Adolphus, Gustavus II

WordNet sense 6 (king of Sweden who established Lutheranism as the state religion (1496-1560)):

Gustavus I