Final answer:
The leader of the 9/11 attacks was Osama bin Laden, who founded the extremist group al-Qaeda. Khalid Sheikh Mohammed was the 'principal architect' of the attacks, helping to plan and organize them. Osama bin Laden was killed by US Navy SEALs in May 2011.
Step-by-step explanation:
The term '911' is most commonly associated with the September 11, 2001, terrorist attacks in the United States. The key figure believed to be the leader of the 9/11 attacks was Osama bin Laden, who was the founder of the extremist group al-Qaeda. This organization planned and carried out the coordinated attacks on the World Trade Center in New York City and the Pentagon in Washington, D.C., leading to the deaths of nearly 3,000 people.
Bin Laden was not on the ground leading the 19 hijackers but directed the operation from abroad. Khalid Sheikh Mohammed is often referred to as the 'principal architect' of the attacks due to his involvement in planning and organizing the details. After the 9/11 attacks, Osama bin Laden became one of the most wanted men in the world, and he was ultimately located and killed by US Navy SEALs in May 2011.