Gustav IV Adolf or Gustav IV Adolph (1 November 1778 – 7 February 1837) was King of Sweden from 1792 until he was deposed in a coup in 1809. He was also the last Swedish monarch to be the ruler of Finland.
The occupation of Finland in 1808–09 by Russian forces was the immediate cause of Gustav's violent overthrow by officers of his own army. Following his abdication on 29 March 1809, an Instrument of Government was hastily written, which severely circumscribed the powers of the monarchy. The "Instrument" was adopted in 1809 on 6 June, the National Day of Sweden now as well as in his time. It remained in force until replaced in 1974. The crown, now with strictly limited powers, passed to Gustav's uncle Charles XIII, who had no legitimate children; this want of heirs set into motion the quest for a successor, who was found the following year in the person of Jean-Baptiste Jules Bernadotte, the first monarch of the present royal family.