For years, Osama bin Laden’s charisma kept al-Qaeda’s ranks filled with zealous recruits.

But it was the strategic thinking and the organisational skills of his Egyptian right-hand man that kept the terror network together after the United States invaded Afghanistan in 2001 and pushed al-Qaeda out.

With bin Laden killed, Ayman al-Zawahri becomes the top candidate for the world’s top terror job.

It’s too early to tell how exactly al-Qaeda would change with its founder and supreme mentor gone, but the group under al-Zawahri would likely be further radicalised, unleashing a new wave of attacks to avenge bin Laden’s killing by US troops in Pakistan yesterday to send a message that it’s business as usual.

Al-Zawahri’s extremist views and his readiness to use deadly violence are beyond doubt.

In a 2001 treatise, Knights Under the Prophet’s Banner, he set down the long-term strategy for the jihadi movement – to inflict “as many casualties as possible” on the Americans, while trying to establish control in a nation as a base “to launch the battle to restore the holy caliphate” of Islamic rule across the Muslim world.

Unlike bin Laden who found his Jihadist calling as an adult, al-Zawahri’s activism began when he was in his mid-teens, establishing his first secret cell of high school students to oppose the Egyptian government of then President Anwar Sadat he viewed as infidel for not following the rule of God.

The doors of jihad opened for him when, as a young doctor, a visitor came to him with an offer to travel to Afghanistan to treat Islamic fighters battling Soviet forces. His 1980 trip to the Afghan war zone – only a few months long but the first of many – opened his eyes to a whole new world of possibilities.

What he saw there, he was to write 20 years later, was “the training course preparing Muslim mujahideen youth to launch their upcoming battle with the great power that would rule the world: America.”