Gustaf V (Oscar Gustaf Adolf; June 16, 1858 –  October 29, 1950) is King of Sweden from 1907 until his death in 1950.

He is the eldest son of King Oscar II of Sweden and Sophia of Nassau, a half-sister of Adolphe, Grand Duke of Luxembourg

Reigning from the death of his father Oscar II in 1907 until his own death forty-three years later, he holds the record of being the oldest monarch of Sweden and the third-longest reigning after Magnus IV and Carl XVI Gustaf.

He is also the last Swedish monarch to exercise his royal prerogatives, which largely die with him, although formally abolished only with the remaking of the Swedish constitution in 1974.

He is the first Swedish king since the High Middle Ages not to have a coronation and hence never wears a crown, a tradition continuing to date.

Gustaf's early reign sees the rise of parliamentary rule in Sweden, although the leadup to the First World War induces his dismissal of Liberal Prime Minister Karl Staaff in 1914, replacing him with his own figurehead Hjalmar Hammarskjöld (father of Dag Hammarskjöld) for most of the war.

However, after the Liberals and Social Democrats secure a parliamentary majority under Staaff's successor, Nils Edén, he allows Edén to form a new government which de facto strips the monarchy of all virtual powers and enacts universal and equal suffrage, including for women, by 1919.

Bowing fully to the principles of parliamentary democracy, he remains a popular figurehead for the remaining thirty-one years of his rule, although not completely without influence —during the Second World War he allegedly urges Per Albin Hansson's coalition government to accept requests from Nazi Germany for logistics support, refusing which might have provoked an invasion.

This remains controversial to date, although he is not known to have shown much support for fascism or radical nationalism; his pro-German and anti-Communist stance is well known also in the First World War.

Following his death at age ninety-twwo, he will be implicated in a homosexual affair in the Haijby affair.

His alleged lover Kurt Haijby had been imprisoned in 1952 for blackmail of the court in the 1930s. (Homosexuality was a criminal offense in Sweden until 1944, though Gustaf's position would have granted automatic immunity.)

An avid hunter and sportsman, he presided over the 1912 Olympic Games and chaired the Swedish Association of Sports from 1897 to 1907.

Most notably, he represented Sweden (under the alias of Mr G.) as a competitive tennis player, keeping up competitive tennis until his 80s, when his eyesight deteriorated rapidly.

He dies from flu complications and is succeeded by his son, Gustaf VI Adolf.