King Abdullah Bin Abdulaziz al Saud, who ruled Saudi Arabia since 1996, has died at the age of 90.
Abdullah's death was announced on Saudi state TV saying the king died late on January 22, but offered few other details.
Abdullah had been in hospital for several weeks suffering from a lung infection.
His successor is his 79-year-old half-brother, Prince Salman, who has recently taken on the ailing Abdullah's responsibilities, according to the official Saudi Press Agency.
Under Abdullah's rule, the oil-rich, ultraconservative Islamic nation faced a growing chasm between fundamentalists and modernizers. While instituting several noteworthy reforms throughout his reign, including measures aimed at economic liberalization, the king was also criticized by human rights group for overseeing repressive government control.
The latter years of his rule were also marked by regional turmoil. The Arab Spring threatened the House of Saud and Saudi Arabia's position as a "guarantor of stability" in the Middle East, prompting Abdullah to take measures to ward off potential discontent at home.
The fall of Egyptian President Hosni Mubarak particularly rankled Saudi Arabia, which accused the West of disloyalty for tacitly accepting regime change.
Later, the arrival of a new threat to the region -- Islamic State (IS) militants -- caused Saudi Arabia to drift back toward the West and to take a leading role in the Arab Coalition assembled to beat back the militants. Speaking to the U.S. broadcaster PBS about the campaign against IS, Abdullah said: "We, as Arab and Muslim countries ... need to take ownership of this."
Women in Saudi Arabia entered 2015 optimistic that they would for the first time have the right to vote in nationwide local elections.
The change came as the result of reforms Abdullah announced in 2011 and, in January 2013, the king appointed 30 women to the 150-member Shura Council for the first time.
Nevertheless, Abdullah's rule was not marked by the significant changes that many Western observers had hoped for and his reforms were criticized as being too slow or merely cosmetic.
In 2012, Human Rights Watch described his government as one of "unflinching repression," decrying abuses of migrant works, arbitrary arrest and torture, heavy press censorship, discrimination against religious minorities, and a closed political system.
Recently, Saudi Arabia has come under criticism for ordering blogger Raif Badawi to 1,000 lashes, to be carried out in public 50 lashes at a time for 20 weeks.
Abdullah was born in Riyahd in 1924 to a Bedouin mother and Saudi Arabia's founding King Abdul Aziz Al Saud.
After receiving a formal religious education, he was appointed commander of the Saudi Arabian National Guard in 1962. While he was ridiculed by many for having a stutter, he kept the post for nearly 50 years.
Key U.S. Partner
In 1996, at more than 70 years of age, Abdullah became the de facto ruler of the country after his half-brother, King Fahd, was incapacitated by a stroke.
When he officially ascended the throne in 2005, King Abdullah inherited a country where the ultraconservative Wahhabi establishment, which had long helped preserve the power of the royal family, faced increasing calls for reform.
After the emergence of Al-Qaeda in the 1990s; the September 11, 2001 attacks against the United States, in which 15 of the 19 hijackers were Saudis; and a later violent insurgency in the kingdom itself, the royal family recognized that religious extremism was threatening its own grip on power.
"I'm hoping from you and I repeat that if any word or news reaches you of any person who you sense has deviated -- deviated from religion or attacked religion -- or is an extremist, you must stop them and bring them to me personally," he said in June 2004.
Under his rule, Riyadh remained one of the West's, and especially Washington's, key partners in the Arab World.
However, he did not allow the United States or its allies use its soil -- viewed by many of the world's more than 1 billion Muslims as the holy land of Islam -- to launch strikes in Iraq and Afghanistan.
As a pro-reform movement rumbled through the Arab world in 2010 and 2011 the king vowed to pursue a program of social, economic, and political reforms.
He ordered the establishment of a state authority to fight corruption and announced economic benefits worth tens of billions of dollars aimed at solving chronic unemployment and housing shortages.
But there were harsher responses to the Arab Spring as well. Saudi Arabia responded to a series of protests by the kingdom's Shi'ite minority in the oil-producing eastern province by banning all protests and marches. Authorities arrested hundreds of people demanding political and social change and sentenced prominent reformists to long sentences.
In his later years, King Abdullah strove to counter the rising influence of Shi'ite Iran across the Middle East. In a 2009 diplomatic cable released by WikiLeaks, he was quoted as urging the United States to "cut off the head of the snake" by attacking Iran.
In 2014, a year before his death, Forbes listed the king among the world's richest royals, with a fortune of more than $20 billion.
He suffered increasingly from spinal problems in the years before his death and was hospitalized with a lung infection in early January, 2015.
The king will be laid to rest after the noon prayer on January 23 in the city of Riyadh.
He is succeeded by Crown Prince Salman, who has served as governor of the Riyadh for decades and has held the post of defense minister.
Abdullah had more than 30 children from around a dozen wives.