(Bloomberg) –Sultan Qaboos bin Said, the Omani leader who turned an isolated Middle Eastern country torn by civil war into a stable oil exporter and an ally to both the U.S. and Iran, has passed away at age 79.

The Sultan’s death happened on Friday and was announced by the official Oman News Agency. His death follows a years-long struggle with an illness widely speculated to have been colon cancer and ends almost half a century of rule over a nation strategically located near key oil shipping lanes at the eastern tip of the Arabian Peninsula.

There’s no designated heir as Qaboos had no known brothers or children, prompting analysts to expect one of his cousins will eventually succeed him in a so-far secret palace transition. Oman’s Defense Council has invited the royal family to convene to choose a successor, state TV reported.

Qaboos set himself apart from his peers in the Gulf with an unorthodox regional policy that saw Oman refuse to join the Arab League in sanctioning Egypt after it established relations with Israel in 1979, and then go on to become the first Gulf state to forge trade ties with the Jewish state 17 years later. He kept his Gulf Cooperation Council neighbors at arm’s length, shunning their annual summits in his later years and refusing to follow Saudi policies toward Yemen, Iran and Qatar.

During his rule, Oman instead often served as a neutral mediator in the region, earning it a “Switzerland of the Middle East” moniker. It sponsored cease-fire talks during the Iran-Iraq War in the 1980s, and hosted secret discussions between the U.S. and Iran that paved the way for the landmark nuclear deal in 2015. The sultanate didn’t participate in the Saudi-led boycott of Qatar from 2017, and saw its trade with the gas-rich nation soar.

“This impressive feat was done without antagonizing other nations,” said Gary Grappo, a former U.S. ambassador to the country. “His sultanate rightly became known as an island of stability in a very troubled region.”

At home, Qaboos gave women the vote in the early 1990s and enabled them to stand for public office, unprecedented moves for the Gulf, while retaining total control over major political decisions.

Fading Allure

In recent years, though, the quiet repression of activists and independent media became routine, and the achievements of his early years faded from memory for a new generation who complained about corruption as well as economic and political stagnation.

The call for loyalty to Qaboos “has proved inaudible in a country where 84% of the population was born after 1970 and 70% after 1980,” wrote Marc Valeri of the University of Exeter in an article on the ruler.

In 2011, Oman experienced its first protests in decades as part of the wave of unrest in the Arab world, and at least two people were killed in clashes while dozens were detained. The ruler fired some officials, granted more powers to the elected consultative council, gave cash handouts and pledged tens of thousands of jobs. The solutions were criticized as being cosmetic.

Qaboos was born on Nov. 18, 1940, in Salalah, southern Oman, according to his official biography. He attended school in Oman and England before entering the U.K.’s Royal Military Academy at Sandhurst.

After graduating, he joined the British Army and served in Germany for a year. In the 1960s, he returned to Oman, then under heavy British influence, but was kept under virtual house arrest by his father, Said bin Taimur, who had become increasingly reclusive and paranoid.

Qaboos was just 29 when he overthrew his father in a 1970 palace coup supported by London and aided by Oman’s British-controlled armed forces. The U.K. saw the older monarch as an inept leader unable to deal with the insurgencies the country faced. In 1976, Qaboos married a cousin, but they were soon divorced.

Music Lover

Using bountiful oil revenue, Qaboos transformed a country with barely any paved roads into an independent nation of 4 million people with a $79 billion economy. Producing a little under a million barrels of oil a day, Oman is the Middle East’s largest oil and natural-gas producer that’s not a member of the Organization of Petroleum Exporting Countries.

As energy wealth enriched Oman, he boosted spending on health and education while opting out of the race among Gulf neighbors to build the tallest skyscraper or biggest mall. Oman’s capital, Muscat, is a quiet city of low-rise buildings suspended between rocky mountains and the sea.

A lover of classical music, Qaboos founded the Royal Oman Symphony Orchestra in 1985. He also was said to enjoy riding and shooting.

The monarch solidified his rule, putting his name on major monuments and in the country’s national anthem while quashing internal dissent.

The sultan did little to change Oman’s political system of absolute monarchy, with major decisions implemented by royal decree. He clashed with his uncle Tariq bin Taimur, who favored a constitutional monarchy and served as prime minister from 1970 to 1971, before he resigned and Qaboos took that position for himself.

‘Reclusive and Lonely’

The written constitution Qaboos introduced requires the ruling family to choose a successor within three days of the throne falling vacant. Should it fail to do so, a successor designated by Qaboos in a letter to the family council will be installed. It’s widely believed that one of three cousins — sons of Tariq — will most likely become the sultan.

“The biggest challenge of his successor? He won’t be Qaboos,” said ambassador Grappo. “With the possible exception of Lee Kuan Yew of Singapore, it’s hard to imagine another leader who’s had greater impact on his nation than Qaboos has had in Oman. It’s inestimable.”

J.E. Peterson, a historian who has written on Oman and its leaders, said that “50 years of governing alone at the top seemed to leave” Qaboos “reclusive and lonely. But his vision for his country, even though not perfect, seems likely to determine Oman’s orientation well into the future, no matter who succeeds.”

–With assistance from Zaid Sabah.