of the al-Qaeda terrorist network (2011– ). He studied medicine at Cairo University and then served in the Egyptian army. Involved in militant Islamist activity since his teenage years, he was imprisoned (1981–84) following the assassination of Anwar al-Sadat. He then travelled to Saudi Arabia, Pakistan, and Afghanistan, where he met Osama Bin Laden. In the early 1990s al-Zawahiri became leader of the Islamic Jihad militant group, which merged with al-Qaeda in 2001. He was closely involved in the September 11 attacks on the USA and in the following years gradually assumed the practical leadership of al-Qaeda as Bin Laden was forced into hiding. He became the formal leader after Bin Laden’s death in 2011.