Gustavus III., king of Sweden, eldest son and successor of King Adolphus Frederick and Ulrica Louisa, princess of Prussia, born in Stockholm, Jan. 24,1746, died there, March 29, 1792, He was educated under the superintendence of Counts Tessin and Scheffer. His ambitious tendencies early awakened the anxiety of these noblemen, who vainly attempted to restrain and correct his disposition. On his accession to the throne, Feb. 12, 1771, the state was divided between two sordid and corrupt factions. They were the "Hats" and "Caps," or "France and Commerce," against "Agriculture and Russia." Under Adolphus the Hats had obtained the predominance, and proposed to subvert the constitution by force, and to rescue the country from the domination of the nobles. Gustavus, who at the time of his father's death was travelling on the continent, procured from the French government a promise of aid and support against the aristocratic party. Hastening to Sweden, he labored to obtain popularity, while his emissaries propagated disaffection to the diet. Having matured his scheme, Gustavus confided the secret to a favorite officer, Hellichius, who shut the city gates of Christianstad, and published a manifesto against the diet.
The place was immediately invested by government troops, while Stockholm was declared under martial law. Gustavus, having secured the support of the troops, posted a guard over the assembled senators, harangued the people on the great square, entered the hall with a strong guard, and produced a new constitution, which was immediately approved and confirmed by subscription and oath. The diet acquiesced; and thus, on Aug. 21, 1772, without the loss of a single life, a revolution was accomplished. The government he created was better than that of the oligarchy he had overthrown, though the royal power was increased. In 1783 he went abroad again, visited Italy, and passed some time in Paris. During his absence a famine made great havoc, the people were disturbed, the nobility rose against him, and the diet forced him to make concessions. The king, who in 1772 was the idol of the nation, had become in 1787 an object of detestation. War was now employed to stimulate loyalty. Gustavus secretly ordered a march upon St. Petersburg, and, having quelled an uprising of the nobles, secured extraordinary powers, and at the head of a body of Dalecarlian peasants repulsed the Danes who menaced Gothenburg, he began in person a vigorous campaign against Russia. The war continued with varying success for upward of two years, and was terminated by a peace on terms honorable to Gustavus after the Swedish naval victory of Swenkasund, July 9 - 10, 1790. Dissatisfied, however, with the result of the war, he resolved to take part in restoring the power of Louis XVI., and aimed at heading a Swedish, Russian, Prussian, and Austrian coalition for the invasion of France. He went to Spa and Aix-la-Chapelle to concert measures, but before his plans were matured he was shot at a bal masque in Stockholm by Anckarstroem, the instrument of a conspiracy of nobles.
Gustavus lingered 13 days after receiving the fatal shot. He was a man of great ability, but capricious and insincere. He was the author of dramatic works and lyric poems, published in Swedish in Stockholm in 1806-'12 in 6 vols., and also in French. On June 23, 1788, before his departure for the Finnish war, he deposited two boxes in the library of Upsal, requesting that they should only be opened 50 years after his death. They were opened March 29, 1842, and found to contain historical and literary essays and letters, which were published by Geijer (3 vols., Upsal, 1843-'6), and translated into German.