Born in 1940, Qaboos was sent abroad for his education to Britain, attending the elite Sandhurst Royal Military Academy from where he graduated in 1962.
He went on to join a British infantry battalion in Germany, returning home to bide his time under the close watch of his father, Sultan Said bin Taymur.
Qaboos transformed Oman during his 49-year reign from a poverty-stricken country torn by dissent into a prosperous state and an internationally trusted diplomat.
Oman has maintained neutrality in many recent regional conflicts, such as the war in Yemen, and has been an effective mediator between rivals in the Middle East.
Qaboos became sultan in July 1970 after deposing his father in a palace coup – aided by the British – with the aim of ending the country’s isolation and using its oil revenue for modernisation and development.
With no successor, analysts fear a resurgence of tribal rivalries and political instability at a time when rifts are growing with neighbouring Saudi Arabia and the United Arab Emirates.