Hassanal Bolkiah, one of the world's longest-reigning monarchs, became sultan in October 1967 after his father, Sir Haji Omar Ali Saifuddin, abdicated. He was crowned in August 1968.
In 1991 he introduced a conservative ideology called Malay Muslim Monarchy, which presented the monarchy as the defender of the faith.
Apparently aimed at pre-empting calls for democratisation, it is said to have alienated Brunei's large Chinese and expatriate communities.
In September 2004 the sultan reopened Brunei's parliament, 20 years after it was suspended. Observers said it was a tentative step towards giving some political power to the country's citizens.
The sultan was born in 1946 and was educated in Malaysia and Britain. He has two wives and is one of the world's richest individuals.