He ascended the throne on the death of his grandfather, King Gustaf VI Adolf on 15 September 1973.
Following the death of Gustav 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 4.
A short while after he became King in 1973, the new 1974 Instrument of Government took effect, formally stripping him of any formal role in the legislative process, and several other duties normally accorded to a head of state, such as the formal appointment of the prime minister, signing off legislation, and being commander-in-chief of the nation's military.
The king's heir apparent, upon passage on 1 January 1980 of a new law establishing absolute primogeniture (the first such law passed in European history), is Crown Princess Victoria, the eldest child of the king and his wife, Queen Silvia.
Carl Gustaf is the 2nd longest-reigning monarch in Swedish history, having overtaken King Gustaf V in 2016. He was the youngest of five children and the only son of Sweden's Prince Gustaf Adolf and Princess Sibylla.
He was christened at the Royal Chapel on 7 June 1946 by the Archbishop of Uppsala, Erling Eidem.
He was baptised in Charles XI's baptismal font, which stood on Gustav III's carpet and he lay in Charles XI's cradle with Oscar II's crown beside him.
Afterwards, he appeared before the parliament, diplomatic corps, court, etc.
in the Hall of State at the Royal Palace where he gave a speech.
In addition, he closely studied the affairs of the Riksdag, Government, and Ministry for Foreign Affairs.
The Crown Prince also spent time at the Swedish Mission to the United Nations and the Swedish International Development Cooperation Agency (SIDA), worked at a bank in London, at the Swedish Embassy in London, at the Swedish Chamber of Commerce in France, and at the Alfa Laval Company factory in France.
Princess Eugenie will move into Kensington Palace with Mr Brooksbank after their marriage.