Carl XVI Gustaf is the King of Sweden. He ascended the throne on the death of his grandfather, King Gustaf VI Adolf, on 15 September 1973. He is the youngest child and only son of Prince Gustaf Adolf, Duke of Västerbotten, and Princess Sibylla of Saxe-Coburg and Gotha. His father died on 26 January 1947 in an airplane crash in Denmark when Carl Gustaf was nine months old. Upon his father's death, he became second in line to the throne, after his grandfather, the then Crown Prince Gustaf Adolf. Following the death of his great-grandfather King Gustaf V in 1950, Gustaf Adolf ascended the throne and thus Carl Gustaf became Sweden's new crown prince and heir apparent to the throne at the age of four.

A short while after he became king in 1973, the new 1974 Instrument of Government took effect, formally stripping Carl XVI Gustaf of even a nominal role in governmental affairs. As a result, he no longer performs many of the duties normally accorded to a head of state, such as the formal appointment of the prime minister, signing off on legislation, and being commander-in-chief of the nation's military.

The king's heir apparent, after passage on 1 January 1980 of a new law establishing absolute primogeniture (the first such law passed in Western European history), is Crown Princess Victoria, the eldest child of the King and his wife, Queen Silvia. Before the passage of that law, Crown Princess Victoria's younger brother, Prince Carl Philip, was briefly the heir apparent, as of his birth in May 1979.

Source: Wikipedia - Carl XVI Gustaf