After completing his studies, Azzam moved to Jordan and joined Palestinian nationalists fighting Israel. However, he was disillusioned by the PLO, whose leaders spent their spare time gambling and drinking. He moved to Jeddah in Saudi Arabia to lecture at the King Abdul-aziz University, a hotbed of radicalism where exiled members of the Muslim Brotherhood from neighbouring states regularly found refuge, and where Azzam first met bin Laden.

When Azzam left Saudi Arabia for Afghanistan in 1979, he initially moved to Islamabad University. He soon decided to dedicate himself to the jihad full time and to create a channel for Arab fighters who wanted to join him. Before the Hajj that year, he visited America to enlist new fighters and raise funds.

I interviewed Jalal Abualrub, a Palestinian who had been studying in the US in 1979 and who helped Azzam visit more than 50 US cities, spreading the word about the Afghan jihad and raising funds. Jalal explained that Azzam's subsequent trip to Mecca to have his fatwa about jihad endorsed by Saudi Arabia's Grand Mufti and other Wahhabi scholars inspired him and many others to go to Afghanistan. "Having the backing of the scholars was very important," Jalal explains. "Once we had that there was nothing stopping us." The trickle of foreign fighters entering Afghanistan became a flood.

Another Azzam protégé, Abdullah Anas (who later became Azzam's son-in-law), was a young imam in Algeria when he first read about Arab volunteers going to join the Afghan struggle. "I went for pilgrimage in 1984 and bumped into Abdullah Azzam entirely by chance," he recalled over coffee in West London. "I asked him whether the jihad in Afghanistan was a duty and whether the Saudi scholars had backed it. He told me, ‘Yes', and I decided to go immediately."

Within weeks, Anas had arrived at Azzam's house in Islamabad and was introduced to a man calling himself Abu Abdullah; he was a tall, slim man with a flowing beard and pointed features. Abu Abdullah turned out to be the nom de guerre of bin Laden. Anas joined Azzam and bin Laden to create the "Services Bureau", which organised travel and accommodation for Arab fighters before sending them to join training camps in Afghanistan.