By Mike Collett-White

LONDON, April 25 (Reuters) - A new book looks at Osama bin Laden through the prism of his family, and suggests that the death of his extrovert playboy brother Salem in a 1988 plane crash was an important factor in his radicalisation.

"The Bin Ladens", by Pulitzer Prize-winning author Steve Coll, traces the family's rise to prominence in Saudi society through the 20th century and how its fate, and that of Osama in particular, was inextricably linked with the royal family's.

By putting Osama's life in the context of his 53 globetrotting brothers and sisters and the upheavals facing Saudi Arabia, Coll seeks to dispel some of the myths surrounding a man often portrayed in the West as an incarnation of evil.

Osama was around nine years old when his father died in a plane crash in 1967. While immersing himself in Islamic studies at school, the boy found new father figures in radical mentors who later introduced him to the idea of "transnational jihad".

His elder half-brother Salem was a very different character: a larger-than-life, jetsetting playboy who took over the family business and wooed the Saudi royals with his boyish charm.

The reward was construction contracts in the kingdom and a family fortune that was crucial to Osama's role as mastermind of the 9/11 attacks on the United States in 2001.

While the brothers followed different paths, underlining the tensions in Saudi Arabia at the time between a pious past and the new allures of the West, Salem remained an important influence over Osama and the bin Laden clan throughout his life.

The keen pilot's death in 1988 in a flying accident left the dynasty adrift, and contributed to Osama's growing rifts with his family and with the Saudi authorities, Coll argues.

It also came at a time when the Soviet occupation of Afghanistan was winding down, encouraging Osama and other radical leaders to consider a broader armed struggle.

"I met so many friends of Salem who, without prompting, said if he had lived, 9/11 would not have happened, and you can see their case," Coll explained in an interview with Reuters.

"You can just imagine at that moment in the early 90s ... Salem would just have figured out a way to bring him back in."

AFGHAN ADVENTURES, FAMILY RIFTS

Coll was referring to the period when Osama began to quarrel with the Saudi authorities, partly because of his backing for Islamist militants in Yemen and partly due to the deployment of U.S. troops on Saudi soil after Saddam Hussein invaded Kuwait.

After moving to self-imposed exile in Sudan, he became increasingly critical of the Saudi royal family. His brothers, who lacked Salem's charm and influence, were unable to rein him in and eventually disowned him as an embarrassment.

Osama's eldest son abandoned him for Saudi Arabia and a growing sense of isolation probably added to his radicalisation.

"A hint of King Lear in the wilderness began to enter Osama's exile," Coll writes.

In the early 1980s Osama had begun travelling to Pakistan, where his wealth brought him influence among Islamic radicals backing the anti-Soviet Afghan insurgency.

There he was actively supported by Salem, who was keen to help his brother and serve the royal family's clandestine foreign policy in the region at the same time.

Osama moved to Peshawar near the Pakistan-Afghan border in 1986. He became increasingly involved in the rebellion, travelled to London to discuss buying missiles, saw battle first hand with his band of Arab volunteers -- and set up al Qaeda.

According to Coll, Osama's success at building the radical network stemmed partly from his ability to attract members from a diverse range of nationalities and like-minded movements.

Similarly his father employed Italian engineers and U.S. accountants to build the bin Laden empire and had "a labour force that was as diverse as any in the Gulf at the time."

Osama embraced technology by using satellite phones to coordinate his militant activities at about the same time his family was investing in a pioneering satphone venture.

He also made videos and audio tapes for television and the Internet which revealed something of the showmanship for which his late brother Salem was renowned.

(Editing by Mark Trevelyan)

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