Crown Prince Nayef, who died on Saturday, built the formidable security force which crushed an Al Qaeda revolt in Saudi Arabia and with it any dissent against his family's century-old grip on the world's leading oil exporter.

To liberals, Nayef, a son of the state's founder, was the forbidding face of a conservative establishment that opposed any real moves toward democracy or greater women's rights, oversaw the fearsome religious police and for years headed an Interior Ministry which imprisoned political activists without charge.

But former diplomats, local journalists and members of the ruling house described him as a more flexible man in private, who survived more than three decades at the centre of a Saudi political system.

'Nayef is widely seen as a hardline conservative who at best is lukewarm to King Abdullah's reform initiatives,' said a 2009 US diplomatic cable about the prince, who was in his late 70s.

'However, it would be more accurate to describe him as a conservative pragmatist convinced that security and stability are imperative to preserve al-Saud rule and ensure prosperity for Saudi citizens,' said the cable, published by WikiLeaks.

His main concern was battling Al Qaeda in the kingdom and in neighbouring Yemen and maintaining a strong barrier against Shi'ite arch-enemy, Iran, according to US embassy assessments.

Nayef was regarded as closer than many of his brothers to the hardline Wahhabi religious establishment whose support had been vital to his father's establishment of the state in the early 20th century. As a result, he enjoyed particular favour from the clergy who provide legitimacy to the royal house.

Nayef was born in around 1933 in Taif, the mountain town where the royal court would annually retreat to each year from the stifling summer heat of the desert capital Riyadh and the Red Sea port of Jeddah, the kingdom's second city.

Saudi Arabia had only a year earlier come into being as a state. Nayef's father King Abdulaziz Ibn Saud, over the course of the preceding 30 years of warfare and diplomacy, had united the Bedouin tribes behind his vision of a pure Islamic state.

He conquered much of the Arabian peninsula, securing his family's control over Islam's holiest sites at Makkah and Madinah.

Growing up in the royal court of the 1930s and 1940s, Nayef is of the last generation of Saudi leaders who knew the austere desert kingdom before the first flush of oil wealth changed it beyond all recognition and let royal relatives live spendthrift lives abroad in the luxury stores and fleshpots of the West.

A son of Ibn Saud by his favourite wife Hassa bint Ahmed al-Sudairi, Nayef was one of seven of her sons who were groomed young for high office and formed their own power bloc within an extended family that included nearly 40 other half-brothers.

Nayef's own son, Prince Mohammed bin Nayef, a well regarded deputy interior minister in the current administration, headed Saudi efforts to root al Qaeda from the kingdom.

Named governor of Riyadh aged only 20, Nayef impressed his father and went on to become interior minister in 1975 where he was soon known as an ally of the Wahhabi clerics who had run the palace school of his childhood.

It was this ministerial role that came to define Nayef by giving him responsibility for protecting the kingdom from internal threats - most frequently from Islamist militants.

'Given his paramount concern with maintaining stability, Nayef's instincts tend towards concessions to religious demands, especially on cultural-social issues,' said the leaked US appraisal of him in 2009.

'This is sometimes misinterpreted as opposition to reform, but more likely stems from a desire to balance competing social forces.'

As the man to whom regional governors answered, Nayef personally handled the petitions of individual Saudi citizens on a daily basis, cultivating a network of supporters across a kingdom where tribal and regional ties still matter.

Despite his fierce reputation atop the internal security forces, Nayef was said by princes to be among the kinder members of the al-Saud dynasty, treating nephews and nieces of the younger generation with more consideration than his peers.

That avuncular side to his character contrasted with the image he sometimes showed to foreign diplomats, who described him as prickly and, in the US appraisal, stiff, slow and shy, despite occasional flashes of 'impish' humour.-Reuters