Oman’s ruler, Sultan Qaboos bin Said, who took power in a 1970 palace coup against his father and then guided the country from medieval-style feudalism toward the embrace of globally oriented policies that hastened modernization and broadened the country’s political influence, died Jan. 10 at 79.

The state-run Oman News Agency announced his death on its official Twitter account but did not disclose further details. Qaboos had left Oman temporarily at least twice since 2014 to receive treatment in Germany for undisclosed medical issues, and he traveled to Belgium for a medical checkup last month.

The death of the longest-serving ruler in the Arab world, and one of the world’s longest-ruling autocrats, opened issues of succession in Oman, which occupies the southeastern corner of the Arabian Peninsula. The country also holds a strategic enclave across from Iran at the Strait of Hormuz, a narrow waterway at the mouth of the Persian Gulf and the route for tankers carrying about one-sixth of the world’s oil supply.

Without children or brothers — Oman does not permit one of his sisters to rule — Sultan Qaboos had no direct heir. He refused to publicly name a possible successor from within his clan, which has ruled Oman for nearly 250 years.

But a successor was quickly announced by Oman state television: Haitham bin Tariq al Said, who served as the sultan’s culture minister.

Sultan Qaboos (pronounced KAH-boos) was born on Nov. 18, 1940, and he was the only son of Oman’s ruler, Sultan Said bin Taimur. His childhood was lonely and cloistered, and his father was mostly absent. He grew up in a palace, able to access books and records but otherwise forbidden from talking to his teachers about anything but his studies. He was prohibited from playing in the sea, just yards from his home.

His father had led the country since the early 1930s and kept it as it had been for centuries: Most of the capital, Muscat, was lit by lanterns at night, there were only a few miles of paved roads, and slavery was permitted. Oman’s status in the world was largely defined by its place in legend as the home of Sinbad, its modest exports of aromatic frankincense, and its colorful turbans influenced by centuries of trade with South Asia and East Africa.

Said bin Taimur grew increasingly cut off from his subjects, especially after an assassination attempt in 1966. His son had been sent to Britain at 16, where he attended the Sandhurst military academy and briefly served in the British army. Upon his return to Oman in 1964, he lived under virtual house arrest under orders from his paranoid father. He grew increasingly frustrated with his father’s policies of isolation and his utter rejection of modernity despite oil resources.

In 1970, he deposed his father in a coup backed by Britain, which had a stake in Oman’s oil fields and sought a freer hand to put down rebel factions in the country. The new ruler presented himself in public, symbolizing a new era for the nation’s 750,000 inhabitants, who had not seen its sultan in person for years or even decades.

“Despite our oil revenues, my father kept the country in poverty,” he said in a rare interview at the time. Said bin Taimur was exiled to Britain and died in 1972.

“Qaboos was really a nation-builder,” said Abdullah Baabood, an Omani native and professor of gulf regional studies at Qatar University. “He took a place of tribal rivalries and a patchwork of regions and gave it a sense of nationhood.”

Sultan Qaboos also leaves a country that has followed — but not entirely mimicked — the stunning metamorphoses across the gulf Arab states.

He shunned the skyscrapers and extravagances of nearby Dubai and Abu Dhabi, stressing that Muscat and other cities should generally retain their traditional character and architecture as much as possible, even as five-star resorts and international brands moved in.

While other gulf states tried to outshine one another with malls and theme parks, Oman concentrated on cultural firsts for the region. Among them: a world-class opera house inaugurated by Plácido Domingo conducting Puccini’s “Turandot,” and a symphony orchestra that reflected the sultan’s lifelong appreciation for music and his interest in the lute and pipe organ.

Countries such as Qatar and the United Arab Emirates hired teams of branding consultants and built world-spanning airlines. Sultan Qaboos was content to cultivate cottage industries such as building traditional wooden sailing vessels, known as dhows, and reviving the tradition of Arab perfume-making with a high-end fragrance house, Amouage.

In November 2014, as the sultan was receiving medical care, he put his imprimatur on a new magazine dedicated to the Arabian camel.

In Washington, Oman maintains the Sultan Qaboos Cultural Center, whose missions include funding scholarships for Americans to study in Oman.

Sultan Qaboos shared one overriding trait with other gulf region leaders: a tight grip on power that allowed no room for dissent or open political debate. And, like several other rulers in the region, he was forced into rare concessions by unrest inspired by the Arab Spring.

In 2011, protests broke out in Oman calling for more job opportunities for young people, in a country where nearly half the population is under 25. The demonstrations led to unprecedented clashes with security forces. In response, Sultan Qaboos stepped in with promises of 50,000 civil-service jobs and slightly more power for an advisory panel, known as the Shura Council.

Still, the reforms only went so far. Anyone daring to challenge authority risked arrest, including crackdowns for social media posts.

Sultan Qaboos and his handpicked inner circle continued to climb in importance for Washington as middlemen for dealings with Iran.

Oman negotiated the release of three Americans who were detained by Iran in 2009 along its border with Iraq and charged with espionage. Oman also played other important messenger roles, including during U.S.-led talks on Tehran’s nuclear program and in helping free 15 British sailors captured by Iranian naval forces in 2007.

At the same time, Sultan Qaboos fostered close ties with Iran both publicly and away from official channels.

Near the Strait of Hormuz, the sultan’s security forces turned a blind eye to Iranian smugglers carrying goods such as televisions and ovens across the Persian Gulf on speedboats. In March 2014, Oman signed a 25-year accord to import Iranian natural gas.

The high-profile diplomacy and dealmaking did little to open a window into the private life of the sultan.

He was perhaps the most enigmatic figure in the fraternity of gulf leaders. Sultan Qaboos, who favored traditional robes and occasionally donned a ceremonial dagger, did not seek another wife after a brief marriage to a cousin, Nawwal, in the 1970s. He mostly eschewed international travel in favor of his palaces in Muscat and Salalah, a southern port with lush flora fed by the Indian Ocean monsoons.

Sultan Qaboos shared little of his personal or political life in public, but leaked U.S. diplomatic cables offered some hints about his priorities. They stressed the need for education, greater participation of women in civic affairs and Oman’s goal of diversifying its oil-based economy.

He displayed a long-range view of regional affairs, at times noting the growth of al-Qaeda’s Yemen-based branch as the top security challenge for years to come. He also took a pragmatic approach to Iran.

“Iran is a big country with muscles and we must deal with it,” he was quoted as saying in a 2008 State Department cable made public by the anti-secrecy group WikiLeaks.

A devoted Anglophile much of his life, Sultan Qaboos also showed increasing openness to Washington.

In 1979, he permitted U.S. forces to use an Omani air base as the staging ground for a failed attempt to rescue Americans held at the U.S. Embassy in Tehran, according to a Congressional Research Service report.

After the Sept. 11, 2001, terrorist attacks, Oman served as a base for U.S. warplanes during the initial U.S. military push into Afghanistan, media and research reports said. Several years later, then-Vice President Richard B. Cheney went fishing aboard the sultan’s yacht.

In a rare 2008 interview with Kuwait’s Al-Seyassah newspaper, Sultan Qaboos waxed poetic on what he called Oman’s “renaissance” under his rule.

“The sun has risen on our country, and we will regain our previous fame and strength and become a country worthy of respect and appreciation,” he was quoted as saying.