King of Sweden from 1771 to 1792; succeeded his father Adolphus Frederick; he found himself early at conflict with his nobles, and in 1772, supported by popular feeling, imposed a new constitution on the country greatly diminishing their power; Gustavus was an enlightened ruler, but somewhat alienated his people from him by his extravagance and fondness for French modes of life; in 1788 he became embroiled in a purposeless war with Russia; he was assassinated when about to take up arms in behalf of the Bourbon cause against the French Republicans (1746-1792).