Mohamed Atta ( محمد عطا السيد transliteration: Muhammad ʻ Ata as-Sayyid ) (September 1, 1968 – September 11, 2001) was an Egyptian Islamist, a known associate of al-Qaeda, and the ringleader of the 19 hijackers in the September 11 attacks. Atta was at the controls of American Airlines Flight 11 which was the first plane to strike the World Trade Center.

Atta was born in Egypt in 1968 in a small town in the Nile delta. At the age of 10, he moved with his family to the Abdeen section of Cairo. Atta studied architecture at Cairo University, and went to Hamburg, Germany in 1992 to continue his studies at the Technical University of Hamburg-Harburg, where he remained a student until fall 1999. In Hamburg, Atta became involved with the Al-Quds Mosque. At some point, he met Marwan al-Shehhi, Ramzi Binalshibh, and Ziad Jarrah who all became part of the Hamburg Cell. Atta disappeared from Germany for periods of time, spending some time in Afghanistan, including several months in late 1999 and early 2000 when he met Osama bin Laden and other top Al-Qaeda leaders. Atta and the other Hamburg Cell members were recruited by Bin Laden and Khalid Sheikh Mohammed for the "planes operation" in the United States. Atta returned to Hamburg in February 2000, reported his passport stolen and obtained a clean passport.

In late March 2000, Atta began contacting flight schools in the United States, inquiring about training. Atta arrived together with Marwan al-Shehhi in June 2000. Both ended up in south Florida at Huffman Aviation where they entered the Accelerated Pilot Program. Atta and al-Shehhi obtained instrument ratings in November 2000, and continued training on simulators and flight training. Beginning in May 2001, Atta assisted with the arrival of the muscle hijackers. In July 2001, Atta traveled to Spain where he met with Binalshibh to exchange information and finalize the plot. In August, Atta traveled on surveillance flights to determine details on how the attacks could be carried out.

In early September, Atta traveled to Maryland, where Hani Hanjour was at the time. Atta then traveled to Boston, and on September 10, he traveled with Abdulaziz al-Omari to Portland, Maine. On the morning of September 11, 2001, Atta and al-Omari flew on Colgan Air back to Boston, where they boarded American Airlines Flight 11. Fifteen minutes into the flight, the team of hijackers attacked and Atta took over control of the aircraft. During the hijacking, Atta made some announcements that were mistakenly transmitted to air traffic control. At 8:46 a.m., he crashed the Boeing 767 into the North Tower of the World Trade Center.