Hassanal Bolkiah, the Sultan of Brunei, came to the throne on 4 October 1967 following the abdication of his father, Sir Haji Omar Ali Saifuddin.
He presides over the tiny state, which is surrounded by the state of Sarawak in Malaysia and abutting the South China Sea.
It has one of the world's highest standards of living thanks to rich oil and gas reserves.
The royal family possesses a huge private fortune
As well as being the Sultan, Bolkiah is the prime minister; heads the defence and finance ministries; is a general in the armed forces; an honorary admiral in the Royal Navy; and a police inspector general.
He lives in the biggest palace in the world, the Istana Nurul Iman, which has 1,788 rooms.