RIYADH The appointment of Prince Muqrin as deputy crown prince sets up the former intelligence chief as next in line to the throne of Saudi Arabia, the world's largest oil exporter, once Crown Prince Salman succeeds King Abdullah.
The youngest son of Saudi Arabia's founder, the prince is an affable former air force captain, diplomats say, and is a close friend of his nephew Prince Bandar, the current spy chief, with whom he served in the military.
An ally of King Abdullah, Muqrin, whom the Saudi embassy in Washington said was born in 1945, has pledged to continue Abdullah's gradual social and economic reforms.
Perhaps unsurprisingly for a member of the Saudi ruling family, which sees itself as locked in a region-wide struggle with Tehran for control of the Middle East, he is seen as hawkish on Shi'ite Iran.
A 2008 U.S. diplomatic cable from the Riyadh embassy, released by WikiLeaks, cited him as being in favor of much stronger sanctions against Iran. In another cable from the following year, he was quoted by diplomats as warning that the Shi'ite crescent was "becoming a full moon".
In February 2013 he was named as second deputy prime minister, a position that has in the past been seen as crown-prince-in-waiting.
Before Thursday's announcement it had been unclear whether Salman would name his half-brother as crown prince or choose his youngest full-brother and former interior minister, Prince Ahmed.
At stake is the future direction of the world's top oil exporter, a country that exerts continuing influence over the world's 1.6 billion Muslims through its guardianship of Islam's holiest sites in Mecca and Medina.
A 2009 U.S. diplomatic cable published by WikiLeaks described Muqrin as having the confidence of the king, who had "given him the lead on Saudi efforts to resolve conflicts in Afghanistan and Pakistan" and sent him to build ties with Syria.
Prince Muqrin trained as a military pilot at Cranston, a British Royal Air Force base, and is described by diplomats as outgoing and gregarious. He served for nearly 20 years as governor of Hail province before being promoted to the post of governor of Medina province in 1999.
He served as intelligence chief from 2005 to 2012, a challenging period when the kingdom put down a determined insurgency by al Qaeda militants and sought to stave off instability from neighboring Iraq, where Islamist armed groups were fighting U.S. occupation.
He is an accomplished musician who plays the lute and takes an interest in astronomy, Saudis say. A Saudi journalist, Fahed Amer al-Ahmadi, told Al Arabiya television the prince spoke several languages and was very "open minded".
The Saudi monarchy does not pass from father to eldest son but has moved along a line of brothers born to the kingdom's founder Abdulaziz ibn Saud.
Although Muqrin is the youngest of this line, and a dozen or so of his elder brothers still live, he is one of the few sons of Abdulaziz who has been seen as qualified to one day become king in a system that prizes experience as well as seniority.
For many years, analysts had assumed Muqrin was out of the running in the kingdom's closely watched succession process because his mother was Yemeni, rather than being from one of the main families of Najd, as the area around Riyadh is known.
That impression was strengthened in the summer of 2012 when he was suddenly replaced as head of the kingdom's intelligence service in favor of his nephew, Prince Bandar bin Sultan, a hawk with close ties to the United States.
However, diplomats said he continued to attend top-level meetings between King Abdullah and visiting foreign leaders, suggesting he remained part of the monarch's inner circle in determining foreign policy.
Some Saudis close the family say it was Muqrin who brought Bandar back into the top echelons of the administration after years when Bandar disappeared from public life.
The 2009 U.S. cable noted Muqrin appeared to have been heavily involved in Saudi dealings with Yemen, and "likely has personal as well as professional reasons for being so" a reference to his Yemeni heritage.
(Reporting by Gulf team; Editing by Janet Lawrence)