His changes looked minute to the outside world. But in a kingdom where ultra-conservative Muslim clerics have long held a lock on all aspects of society, King Abdullah's incremental reforms echoed mightily.

When Abdullah took the unprecedented step of opening a new university where men and women could mix in classrooms, part of his gradual campaign to modernize Saudi Arabia, grumbling arose among the hard-liners who form the bedrock of the powerful religious establishment. One sheikh dared to openly say that the mingling of genders at the king's university was "a great sin and a great evil."

Abdullah sent a tough signal: He fired the critic from the state-run body of clerics who set the rules for Saudi life.

As one of the world's largest oil exporters, Saudi Arabia is governed by a mix of tribal traditions and perhaps the world's strictest interpretation of Islam. Its royal family prefers to act quietly in the background, shies away from direct confrontation, avoids putting itself on the line and prefers slow-paced change to radical reform.

But Abdullah, who died Friday at the age of 90 after nearly two decades in power, acted at times with unusual forcefulness for a Saudi monarch. At home, the results were reforms, including advancements for women, that were startling — for the kingdom at least — and a heavy crackdown against al-Qaida militants. Abroad, his methods translated into a powerful assertion of Saudi Arabia's influence around the Middle East.

Backed by the kingdom's top ally, the United States, the king was aggressive in trying to put up a bulwark against the spreading power of Saudi Arabia's top rival, mainly Shiite Iran, thus shaping the Arab world along new lines — an anti-Iran camp and a pro-Iran camp.

According to a leaked U.S. diplomatic memo, Abdullah urged Washington in 2008 to consider military action against Iran to "cut off the head of the snake" because of its nuclear advances. Another memo spoke of how Abdullah angrily berated Iran's foreign minister in private that "Persians" had no business meddling in "Arab" affairs.

He pushed Gulf allies into taking increasingly vocal stands against Iran and sought to isolate Syria because of its alliance with Tehran.

In Syria, Abdullah stepped indirectly into the civil war that emerged after 2011. He supported and armed rebels battling to overthrow President Bashar Assad and pressed the Obama administration to do the same. Iran's allies Hezbollah and Iraqi Shiite militias rushed to back Assad, and the resulting conflict has left hundreds of thousands dead and driven millions of Syrians from their homes.

Across the multiple conflicts, Sunni-Shiite hatreds around the region took on a life of their own, fueling Sunni militancy. Syria's war helped give birth to the Islamic State group, which burst out to take over large parts of Syria and Iraq. The growing militancy prompted Abdullah to commit Saudi airpower to a U.S.-led coalition fighting the extremists.

In other countries, Abdullah was an iron-willed defender of the status quo, standing against any pressure from the street to change the autocratic Sunni Arab fraternity of monarchs, emirs and sheiks who rule the Gulf region from Kuwait to Oman. He also rushed to the aid of Egypt's military-backed government when it overthrew that country's Islamist president.

He sent Saudi troops to lead a Gulf military force into Bahrain in March 2011 to help the tiny island nation's monarchy crush Shiite-led protests for greater rights. Abdullah also used a mix of largesse and intimidation at home to quell rumblings for change — announcing a more than $90 billion package of incentives, jobs and services in early 2011 while unleashing riot police to crush scattered street demonstrations, particularly by the Shiite minority in the east.

"You could call Abdullah sort of the leader of the anti-Arab Spring," said Ehsan Ahrari, a political analyst in Alexandria, Virginia, who follows Mideast affairs.

Abdullah ultimately strengthened the Saudi alliance with the United States with close cooperation against al-Qaida and against Iran.

President Barack Obama said of the king shortly after his death that "he was always candid and had the courage of his convictions." The statement by the president added that Abdullah's "steadfast and passionate belief in the importance of the U.S.-Saudi relationship" would be part of the king's legacy.

And when there were policy differences with the U.S., Abdullah made them clear. He resisted Washington's pressure to warm to Iraq's U.S.-backed Shiite prime minister, Nouri al-Maliki, seeing him as a mere tool of Iran. He was frustrated with U.S. failure to push ahead the Israeli-Arab peace process, particularly after he won Arab acceptance for his broad plan offering Israel peace with all Arab nations if it withdrew from Arab lands occupied in 1967.

"Once the King has lost trust in a counterpart, his personal antipathy can become a serious obstacle to bilateral relations," noted a 2010 U.S. Embassy briefing for Secretary of State Hillary Rodham Clinton.

"Reflecting his Bedouin roots, he judges his counterparts on the basis of character, honesty, and trust," it said. "He expects good-faith consultations, not surprises."

Abdullah was born in Riyadh in 1924 to one of the many wives of King Abdul-Aziz Al Saud, the founder of Saudi Arabia who reportedly fathered more than 40 children. Abdullah's mother was from a powerful Bedouin tribe known as the Shammar that were rivals with the king's clan, and the marriage was an apparent way to ease the feuds.

Like all Abdul-Aziz's sons, Abdullah had only rudimentary education. His strict upbringing was exemplified by the three days he spent in prison as a young man as punishment by his father for not giving up his seat for a visitor, a violation of Bedouin hospitality.

Tall and heavyset, Abdullah felt more at home in the Nejd, the kingdom's desert heartland, riding his favorite stallions and hunting with falcons. Even as Saudi Arabia was transformed by oil money, Abdullah — who has spoken with a stutter since birth — never appeared comfortable with the trappings of hyper-wealth embraced some of his relatives.

Abdullah rose to be appointed head of Saudi Arabia's National Guard. He was selected as crown prince in 1982 on the day his half-brother Fahd ascended to the throne.

In 1995, he became the kingdom's de facto leader after King Fahd was incapacitated by a stroke. During that time he led national dialogue talks that brought together the country's various factions, tribes and sects to discuss their needs and review their complaints. He took the throne formally in August 2005 after Fahd's death.

His immediate successor, his half-brother Crown Prince Salman, was announced king after Abdullah's death. Salman, at 79, served as defense minister since 2011.

Muqrin was named crown prince. Muqrin, who once oversaw the kingdom's intelligence agency, is the youngest of Abdul-Aziz's sons. Still, he is 69.

In the future, the council will face the potentially divisive question of how to pass the throne down from the aging sons of King Abdul-Aziz to the next generation, the grandchildren. That could potentially put succession and power in the hands of one branch of the family at the expense of the others.

Unemployment remains high among the under-25 generation, which accounts for around half of the population. The Internet and satellite TV — while censored in Saudi Arabia — are rife with criticism and jokes about the country's woes.

His reign opened up small splashes of variety in the kingdom. Shortly after he came to power, color and glitter slowly crept to the all-black abayas women must wear in public. The country's stuffy government-run TV stations started playing music, forbidden for decades. Book fairs opened their doors to women writers and banned books.

His most substantive moves chipped away at the overwhelming restrictions on women in the kingdom. Abdullah for the first time gave women seats on the Shura Council, an unelected body that advises the king and government. He promised women would be able to vote and run in 2015 elections for municipal councils, the only elections held in the country. Two Saudi female athletes competed in the Olympics for the first time in 2012, and a small handful of women were granted licenses to work as lawyers during his rule.

One of his most ambitious projects was a Western-style university that bears his name: King Abdullah University of Science and Technology, or Kaust. Men and women can share classrooms and study together inside the campus grounds, a major departure in a country where even small talk between the sexes in public can bring a warning from the morality police.

But there were limits in how far he would go, given that the royal family's legitimacy is tightly bound up in its alliance with clerics of the hard-line Wahhabi interpretation of Islam, which enforces the strictest segregation of genders in the world and allows public beheadings and floggings.

For example, Abdullah did not respond to demands to allow women to drive — though in 2011 he negated a sentence of 10 lashes handed down by a clerical court on a woman who defied the driving ban. When he died, two Saudi women drivers had been under arrest for more than six weeks after being referred to trial on charges related to their comments on Twitter.

The Sept. 11, 2001 attacks in the United States strained relations between Saudi Arabia and the U.S., where many pointed out that the baseline ideology for al-Qaida and other groups was a radical offshoot of Saudi Arabia's Wahhabi brand of Islam.

But when al-Qaida militants in 2003 began a campaign of attacks in the kingdom aimed at toppling the monarchy, Abdullah cracked down hard. For the next three years, the militants attacked foreign residential compounds, oil facilities and other targets, until security forces succeeded in forcing many of its members to flee to neighboring Yemen, where they revived the branch.

The tougher line helped restore Abdullah's image with the White House. He paid two visits to then President George W. Bush — in 2002 and 2005 — at his ranch in Crawford, Texas.

Abdullah's wealth was estimated at more than $21 billion by some sources, which made him one of the world's richest monarchs. He made a number of humanitarian donations, including relief supplies after the Chinese earthquake in 2008 and donations to refurbish a New Orleans school damaged by Hurricane Katrina in 2005, as well as to Palestinians in the Gaza Strip.

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Keath reported from Cairo.