Saudi Arabia's King Abdullah died early on Friday and his brother Salman became king, the royal court in the world's top oil exporter and birthplace of Islam said in an official statement.
King Salman has named his half-brother Muqrin as his crown prince and heir, rapidly moving to forestall any fears of a succession crisis at a moment when Saudi Arabia faces unprecedented turmoil on its borders.
The rise of Islamic State in wartorn Syria and Iraq has brought to the kingdom's frontiers a militant group that vows to bring down the Al Saud dynasty.
In Yemen, the Iran-allied Shi'ite Houthis have all but seized power and plunged the country to the brink of total chaos, opening space for al Qaeda, which waged an insurgency in Saudi Arabia from 2003-06 and nearly killed a top prince in 2009.
The problems in all those countries are being played out against an overarching backdrop of bitter rivalry between Sunni Muslim Saudi Arabia and its arch regional foe Shi'ite Iran and bumps in Riyadh's key relationship with the United States.
Meanwhile the oil price has more than halved since June, leaving the kingdom likely to face its first budget deficit since 2009 and navigating difficulties with other OPEC members that disagree with its strategy not to defend prices.
Abdullah, said by the Saudi embassy in Washington to have been born in 1924, had ruled Saudi Arabia as king since 2005, but had run the country as de facto regent for a decade before that after his predecessor King Fahd suffered a debilitating stroke.
