Saudi King Salman, who succeeded his half-brother Abdullah on his death on Friday, is a 79-year-old stalwart of the royal family credited with transforming the capital Riyadh during his half-century as governor.

Like Abdullah, Salman is seen as a moderate with a reputation for austerity, hard work and discipline, especially in his role overseeing the hundreds of young princes in the royal family.

Recent years have seen concerns over his health after operations on his back, but Salman took on an increasingly high-profile role as Abdullah's own health issues forced him from the limelight.

Born on December 31, 1935, Salman is the 25th son of the desert kingdom's founder Abdulaziz bin Saud and a prominent member of a formidable bloc of brothers known as the Sudairi seven, after their mother Hassa bin Ahmed al-Sudairi.

He is the sixth son of Abdulaziz to become king of the arid, oil-rich nation.

Salman was appointed governor of Riyadh province at the age of only 20, in line with a tradition of putting royal family members in charge of key provinces.

He is considered the architect of the development of Riyadh from a desert backwater to a modern metropolis, balancing the historic power of the Red Sea city of Jeddah.

The governorship "allowed him to serve as a generally very well respected arbiter of al-Saud family affairs, as well as overseeing the city's emergence," said Eleanor Gillespie of the London-based Gulf States Newsletter.

"Salman has a reputation for probity and for being 'clean' when it comes to money," Gillespie said.

Salman only took on his first ministerial post -- as defence minister -- in 2011 following the death of his brother Prince Sultan.

He was officially named crown prince following the death of the previous heir apparent, Nayef, in June 2012 and undertook a series of visits to Western and Asian nations.

- 'A man of dialogue' -

He has since developed solid ties with foreign partners and "is probably Western policy-makers' favourite choice when it comes to future kings", Gillespie said.

Said to be a hard worker who arrives in the office every day at 7:00 am sharp, Salman also has a reputation for accessibility, holding court three times a week.

"He is a man of dialogue who always preferred to solve problems amicably," said Anwar Eshki, the director of the Jeddah-based Middle East Institute for Strategic Studies.

"He prefers moderation" in internal and foreign policy and "follows in the steps of Abdullah", who was a keen reformer, said Eshki.

Salman is also in charge of the many young princes in the royal family, who "respect and fear him", Eshki said.

Salman is reputed to be ill and there had been speculation he might not claim the throne at all, according to a source close to the circle of power.

But one diplomat said: "Despite his age he is active on all fronts, especially since the king slightly stepped back."

Married three times, Prince Salman had 10 sons, two of whom have died, and a daughter.

One of his sons, Prince Abdul Aziz bin Salman, was appointed assistant petroleum minister in 2004 and is considered likely to succeed veteran Oil Minister Ali al-Naimi.

His most famous son is Prince Sultan, who became the first Saudi to go into space when he joined a 1985 mission on the US space shuttle Discovery. He is currently head of the Saudi Commission for Tourism and Antiquities.