Ayman al-Zawahiri, a former Egyptian physician who joined Osama bin Laden and helped orchestrate the Sept. 11, 2001, terrorist attacks, was killed by an airstrike over the weekend.

What happened: Al-Zawahiri was killed Saturday in Kabul, Afghanistan, by an airstrike conducted by U.S. forces, President Joe Biden announced Monday. Al-Zawahiri was 71 years old. It was the first attack on Afghani soil since the U.S. withdrew last year.

Biden said U.S. intelligence learned earlier this year al-Zawahiri had moved to Kabul to reunite with family, and last week he gave the go-ahead to eliminate the terrorist leader who “carved a trail of murder and violence against American citizens.” Biden said the mission was a success, with no civilian casualties reported.

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Who was Ayman al-Zawahiri? A former physician, he founded the Egyptian Islamic Jihad, a militant group. In the 1990s, al-Zawahiri joined forces with bin Laden and al-Qaida, and helped plan the 9/11 terrorist attacks. He was on the FBI’s most wanted list and eluded capture for more than two decades.

Key quote: “We make it clear again tonight, that no matter how long it takes, no matter where you hide, if you are a threat to our people, the United States will find you and take you out,” Biden said.