Khalid Sheikh Mohammed (Arabic: خالد شيخ محمد‎; also transliterated as Khalid Shaikh Mohammed, and additionally known by at least fifty aliases) (born March 1, 1964, or April 14, 1965) is a prisoner in U.S. custody for alleged acts of terrorism, including mass murder of civilians. He was charged on February 11, 2008, with war crimes and murder by a U.S. military commission and faces the death penalty if convicted.

Khalid Sheikh Mohammed was a member of Osama bin Laden's al-Qaeda organization, although he lived in Kuwait rather than Afghanistan, heading al-Qaeda's propaganda operations from sometime around 1999. According to the 9/11 Commission Report he was "the principal architect of the 9/11 attacks." He is also thought to have had, or has confessed to, a role in many of the most significant terrorist plots over the last twenty years, including the World Trade Center 1993 bombings, the Operation Bojinka plot, an aborted 2002 attack on the U.S. Bank Tower in Los Angeles, the Bali nightclub bombings, the failed bombing of American Airlines Flight 63, the Millennium Plot, and the murder of Daniel Pearl.

Khalid Sheikh Mohammed was captured in Rawalpindi, Pakistan on March 1, 2003, by the Pakistani ISI, possibly in a joint action with agents of the American Diplomatic Security Service, and has been in U.S. custody since that time. In September 2006, the U.S. government announced it had moved Mohammed from a secret prison to the facility at the Guantanamo Bay detention camp. Human Rights Watch, the Red Cross and Mohammed himself have claimed that the American authorities have tortured him, a claim that was supported by information released on February 4, 2008, when it was revealed that he was subjected to waterboarding.