AYMAN AL-ZAWAHIRI

AGE: 55
OCCUPATION: Al-Qaeda's second in command
NUMBER OF TIME COVERS: 0
PREVIOUS APPEARANCES ON THE TIME 100: 1

PRO: An Egyptian and a doctor by training who is widely considered the brains behind al-Qaeda. Wields at least as much influence over the global jihad as does his boss, Osama bin Laden. He has almost certainly played a key role in al-Qaeda's resurgence in the backwaters of Pakistan.

CON: He lives in hiding and last year narrowly escaped a joint U.S.-Pakistan air strike.