Born Ayman Muhammad Rabaie al-Zawahiri on June 19, 1951 in Maadi, Egypt. Born into an upper-class family of doctors and scholars, al Zawahiri was a studious boy who joined his first Islamist group at age 14. He graduated from Cairo University in 1974 and received his master's in surgery in 1978. Click here to read his full biography.

Born Muhammad Ata al Sayyid on September 1, 1968 in Kafr el Sheikh, Egypt. Raised in a suburb of Cairo, Atta received a degree in architecture from Cairo University and a degree in urban planning from the Technical University of Hamburg in Germany. Click here to read his full biography.

Born May 30, 1968 in Morlaix, France. Raised by a single mother, Moussaoui received his master's degree in international business from London's South Bank University in 1995. By 1996, he was meeting with Islamic extremists in London and training in al Qaeda camps in Afghanistan. Click here to read his full biography.

Born May 1, 1972 in the Yemini province of Hadhramaut. Binalshibh worked as a clerk for the International Bank of Yemen from 1987-1995. He moved to Hamburg, Germany, in 1997 where he met Mohamed Atta and joined the al Qaeda cell. Binalshibh trained in the al Qaeda camps in Kandahar, Afghanistan, in 1999, where he became involved in the September 11 terror plot. Click here to read his full biography.

Born March 1, 1964 or April 14, 1965 in the Baluchistan region of Pakistan. Khalid Sheikh Mohammed was raised in Kuwait and joined the Muslim Brotherhood at age 16. He pursued his education in the United States, earning a degree in mechanical engineering from North Carolina Agricultural and Technical State University in 1986. Click here to read his full biography.