Khalid Sheikh Mohammed, who faces charges in connection with the 11 September 2001 attacks in the US, is regarded as one of the most senior operatives in Osama Bin Laden's al-Qaeda network.
The Pentagon says he has admitted to being responsible "from A to Z" for the attacks in New York and Washington.
At a hearing to determine whether he was an "enemy combatant" who should remain in detention at Guantanamo Bay, he also reportedly said he had personally decapitated kidnapped US journalist Daniel Pearl in 2002 and admitted to a role in 30 plots.
He was captured in Pakistan in March 2003 and sent to the US detention centre in Cuba in 2006.
He was indicted in 1996 with plotting to blow up 11 or 12 American airliners flying from south-east Asia to the United States in January, 1995.
According to the transcripts released, the self-proclaimed head of al-Qaeda's military committee admitted to:
He said he had used his own "blessed right hand" to behead Daniel Pearl, according to Pentagon papers.
US university
Mr Mohammed was due to face a military trial at Guantanamo Bay, along with four other suspects in the case. But he is now expected to be moved to New York for a civilian trial in a federal court.
Terror mastermind captured
Official documents have shown that he was subjected to waterboarding - or simulated drowning - 183 times in 2003, before this interrogation technique was banned.
Correspondents say the issue of admissibility of evidence may arise during a civilian trial.
Khalid Sheikh Mohammed is believed to have been born in either 1964 or 1965 in Kuwait into a family originally from the Pakistani province of Baluchistan, which borders Afghanistan.
He is said to be fluent in Arabic, English, Urdu and Baluchi.
He graduated in 1986 from North Carolina Agricultural and Technical State University in the US.
In the late 1980s he moved to Pakistan's north-western city of Peshawar, where he became acquainted with Bin Laden.
Khalid Sheikh Mohammed first achieved notoriety with the discovery of the plot to blow up US airliners over the Pacific in 1995 - known as Operation Bojinka.
The plan was reportedly foiled when police found incriminating computer files during their investigation into a separate plot to assassinate the Pope.
11 September
After the 2001 attacks on Washington and New York which killed more than 3,000 people, US officials raised the reward on his head.
They believe the Kuwaiti co-ordinated the attacks and transferred money that was used to pay for the hijackings.
Mr Mohammed is the uncle of Ramzi Yousef, who was convicted in 1997 of bombing the World Trade Center four years earlier.
The Kuwaiti militant's arrest marked one of the most important breakthroughs in the fight against al-Qaeda.
Terrorism and al-Qaeda expert Rohan Gunaratna described him as a "highly experienced organiser of terrorist attacks across international borders, one of an elite group capable of such events".
It is not just the Americans and the Pakistanis who wanted information from him.
The French magistrate Judge Jean-Louis Bruguiere issued an arrest warrant for him in connection with a suicide bomb attack on a synagogue in the Tunisian resort island of Djerba in 2002.
And the Australians have been interested, because of their investigation into the Bali bombing in 2002 in which 202 people died.
At a pre-trial hearing at Guantanamo Bay in December 2008, Mr Mohammed said he wanted to plead guilty to all charges against him.
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