Al Qaeda leader Ayman al Zawahiri, a founding member of the jihadist movement and one of the key strategists behind an international campaign of terror that culminated in the 9/11 attacks on the U.S., has been killed in a drone strike in Afghanistan, U.S. congressional officials said. He was 71.

From his days as a young medical student who organized underground Islamist cells in Cairo to his years as Osama bin Laden’s top lieutenant in al Qaeda, Zawahiri was a seminal figure of modern jihad as it transformed from a movement seeking to topple authoritarian regimes in the Middle East to waging war on the West.

The shift from local to transnational militancy had cataclysmic results. Zawahiri helped steer the jihadist movement toward a confrontation with the U.S. that he hoped would draw America into costly wars in the Middle East. That strategy led to the 9/11 attacks, which claimed nearly 3,000 lives, and helped prompt the American-led invasions of Afghanistan and Iraq in response, which resulted in the deaths of hundreds of thousands of people.