WASHINGTON: A theologian who rose to prominence in 2005 when he escaped US custody in Afghanistan, Abu Yahya al-Libi became a major motivational figure for al Qaeda, masterminding its propaganda machine.

American officials have described Libi as second-in-command to Ayman al-Zawahiri but security experts say his main value was as an inspirational mouthpiece with the religious credentials other al Qaeda leaders lacked.

A Libyan citizen who spent two years studying in Africa, Libi had a $1 million US price tag on his head before being taken out in a CIA drone strike on Monday in Pakistan's tribal areas, according to US officials.

Libi's role was made clear by the documents retrieved by US commandos from Osama bin Laden's Abbottabad lair, said terrorism expert Bill Braniff.

“One of the things that bin Laden was really struggling with was that individuals were conducting all sorts of really violent attacks but they had sort of lost their way with respect to al Qaeda's original mission,” Braniff, executive director of the START consortium, told AFP.

“So it was very important for bin Laden to have individuals like Abu Yahya al-Libi who could guide the next generation of militants to conduct the right kind of violence.”

Born on January 1, 1963 in Libya, Libi was a relatively unknown militant preacher before his dramatic escape in 2005 from Bagram Air Base in Afghanistan catapulted him into the highest echelons of the organisation.

After picking a lock, Libi and three others reportedly sneaked past their guards to freedom, much to the embarrassment of the United States and its allies—and much to the delight of al Qaeda and its supporters.

His escape quickly attained even more significance as he began appearing in videos for al Qaeda's media arm As-Sahab, promoting the cause and selling the message to a new generation of recruits.

Always wearing a trademark black turban, Libi sometimes traded white robes for military fatigues, depending on his message.

In one video he chastised Muslim scholars for condemning suicide bombings, while in another he urged the faithful to seek revenge for a Danish newspaper's cartoons depicting the Prophet Mohammed.

The former detainee, who picked up Pashto and Urdu, was constantly on the move, shuffling between North and South Waziristan.

He made 17 audio or video releases between 2006 and 2008 outlining al Qaeda's long-term objectives and target preferences, according to the US-based IntelCenter, which monitors militant websites.

“He had theological expertise from al Qaeda's vantage point and he was a huge propaganda piece as a result of all that,” said Braniff.

“Distinguished from a lot of the other militant media or propaganda outlets, As-Sahab was the main line to al Qaeda core's ideology for people that were geographically distributed, and he was the person who was often voicing al Qaeda's messaging.”

The US State Department's Rewards for Justice biography of Libi lists several aliases for the 49-year-old black-bearded Libyan before going on to explain why he merited a reward of up to $1 million.

“Al-Libi is a key motivator in the global militant movement and his messages convey a clear threat to US persons or property worldwide,” it says.

According to the New York Times, Libi went to Afghanistan in the early 1990s before being sent back to study in Mauritania. On his return he toured al Qaeda training camps, preaching militant Islam in a country that had fallen under the control of the extremist Taliban.

He was captured by Pakistani authorities in 2002 and turned over to the Americans before being incarcerated at Bagram.

Informers started giving reports about his presence in North Waziristan in early 2008, placing him in Mir Ali, Datta Khel and Miranshah, three towns that have regularly come under US drone attacks.

Libi, known as a poet and an orator, led a secluded life but was always in the spotlight because of his video speeches.

He was a staunch critic of the Pakistani military, denouncing it as an unholy force of  US paid agents. He is not the second in command, but one of al Qaeda's main ideologues, a scholar, and very popular and influential among al Qaeda recruits,” a Western anti-terrorism official based in Pakistan told AFP on condition of anonymity.

“He is definitely in the top five of al Qaeda. If he was killed, it's another big catch,” the official said, shortly before Libi's death was confirmed.