"With great sorrow and deep sadness. the royal court mourns His Majesty Sultan Qaboos bin Said, who passed away on Friday", the court said in a statement, as discussions on a successor commenced. Oman has also played a conciliatory role between the Houthis and their Gulf enemies, hosting peace talks and facilitating prisoner exchanges. He has sometimes also chaired meetings of the Cabinet.
Under his reign, Oman became known as a welcoming tourist destination and a key Mideast interlocutor, helping the US free captives in Iran and Yemen and even hosting visits by Israeli officials while pushing back on their occupation of land Palestinians want for a future state.
According to the constitution, the royal family council has three days to appoint a new heir after the sultan's death.
Qaboos transformed the Arabian Peninsula nation from a backwater into a modern state while pursuing a moderate but active foreign policy. While other Gulf states have made overtures to Israel, none of their leaders have openly met with Netanyahu.
With global tensions higher than ever following the killing of Iranian general Qassem Soleimani by the USA in Baghdad and ensuing missile strikes by Iran, the death of Sultan Qaboos could not come at a worse time.
One of his first steps as a ruler was to abolish slavery, before setting about using Oman's oil revenues to bring the country into the 20th century.
Small protests broke out in Oman as part of the wider Arab Spring unrest in 2011, revealing discontent over corruption, unemployment and rising prices within the sultanate.
He served in several positions in the Gulf state, including the head of a committee that forged the country's vision for 2040.
He sacked more than a third of the cabinet, created thousands of public sector jobs and paid a dividend to the unemployed, which the International Monetary Fund said amounted to a quarter of Omanis.
Condolences poured in for Sultan Qaboos with Arab and Western leaders praising what they described as his wise rule.
The royal court announced a mourning period that will see businesses and government offices close for three days.
Prime Minister Narendra Modi was among the world leaders who expressed their condolences. Former U.S. President George W. Bush said in a statement that Qaboos had been a stable force in the Middle East. He leaves a profound legacy, not only in Oman but across the region too. "We will forever cherish his contribution to human development through his generosity whose fruits are enjoyed by many in the global community", the President said.
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