Gustavus III., King of Sweden (1746-1792), succeeded his father Frederick Adolphus in 1771. In the second year of his reign he forced the Diet to accept a new constitution, after raising an armed force on the pretext of putting an end to the general disorder. The senators, who had previously been arrested, resigned their usurped powers into the hands of the king. Gustavus, on the whole, showed himself an enlightened ruler, although his extravagant tastes pressed somewhat heavily on the national finances. A war with Russia which broke out in 1788 led to no important results.
Gustavus was preparing to join the league against the French republican government when he was assassinated in the opera-house by Captain Ankarstroem, an agent of the discontented nobility.