Khalid Sheikh Mohammed was al-Qaeda's most ambitious planner and the man more responsible than anyone else for inventing the movement's strategy of spectacular, no-warning, mass casualty attacks.

It was he who, in 1999, came to Osama bin Laden with the idea of hijacking airliners over the United States and crashing them into iconic buildings.

Bin Laden is said to have been deeply sceptical that the plan could work and Mohammed had to spend months persuading his leader that it was viable.

The United States authorities publicly identified him as the planner of 9/11 and placed a $25 million price on his head.

After his transfer from one of the CIA's "ghost prisons" to Guantanamo Bay last year the American authrorities described him as "one of history's most infamous terrorists".

In documents released by the White House at the time, Mohammed was said to have "devoted most of his adult life to terrorist plottings, specifically against the United States". He was further described as "the driving force behind the attacks on 11 September 2001 as well as several subsequent plots against US and Western targets worldwide".

Those other targets included London - where he had ambitions to attack Heathrow airport and blow up Big Ben. Richard Reid, the British shoe bomber in prison in the US, was one of his recuits and he has also been linked to the kidnap and murder in Pakistan of the American journalist Daniel Pearl.

Mohammed was born in 1964 or 1965 in Kuwait but his family originated from the Baluchistan region of Pakistan.

In the 1980s he went to study in the US and graduated in 1986 with a degree in mechanical engineering from North Carolina A & T State University. His studies complete he travelled to Afghanistan to fight with the mujahidin against the Soviet occupying army; three of his brothers are thought to have died in the conflict.

It is thought he first met bin Laden in the Pakistani border town of Peshawar around this time but did not immediately ally himself to the rich Saudi.

When the Soviets left Afghanistan, Mohammed went to south east Asia where he made contact with Islamist groups. While there he devised the Bojinka plot which envisaged blowing up as many as 12 US airliners in-flight over the Pacific.

When that plan was thwarted and he was indicted in connection with it, KSM - as he became known in intelligence circles - disappeared. His familiarity with the West and use of some 30 aliases enabled Mohammed to travel relatively untroubled, often passing himself off as a businessman.

His partner in the Bojinka plot was his nephew Ramzi Yousef who was jailed in 1997 for his role in the bomb attack on the World Trade Centre in New York in 1993.

Mohammed resurfaced in Afghanistan in 1999 when he recognised bin Laden as his emir, or leader, and became a senior figure in the al-Qaeda command structure.

In 2000 Mohammed sent a young British Muslim, Dhiren Barot, to the US to carry out reconaissance on several potential targets including the World Bank, in Washington, and the New York Stock Exchange.

When the security climate changed following 9/11, Barot was moved to London with orders to plan and execute an attack there. He devised two plans which were sent back to Mohammed for his study and approval - using stretch limousines packed with propane gas cylinders as massive car bombs and building a dirty bomb to cause mass panic on the streets of the city.

The plans were discovered on a laptop computer in Pakistan following the arrest of a relative of Mohammed's in 2004. Barot was jailed for life last year after pleading guilty to conspiring to commit murder.

KSM himself was detained in March 2003 when Pakistani police, acting on an intelligence tip-off, raided a house in Rawalpindi and found him asleep in an upstairs room.

His exact whereabouts were unknown for several years until it was revealed that he and a number of other high-profile al Qaeda detainees had been moved to the internment camp at a US Naval base in Cuba.

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