Egyptian-born Al Qaeda terrorist Ayman al-Zawahiri, famed for his role in planning the terrorist attacks on 9/11, began his underground work long before joining forces with Osama bin Laden. Indeed, al-Zawahiri created his first cell (devoted to overthrowing the Egyptian government and replacing it with an Islamic theocracy) in his high school -- when he was just fifteen years old.
Sources
Daniel Cappello, New Yorker, 2002-09-16