Abu Zubaydah, who is thought to have served as Bin Laden's field commander, was captured in Pakistan in March 2002.
The Americans describe him as a "key terrorist recruiter and operational planner and member of Osama Bin Laden's inner circle".
The 30-year-old, who is believed to have been born to Palestinian parents in Saudi Arabia, is also known as Zayn al-Abidin Mohammed Husain and Abd al-Hadi al-Wahab but has used dozens of other aliases.
He has strong connections with Jordanian and Palestinian groups and was sentenced to death in his absence by a Jordanian court for his role in a thwarted plot to bomb hotels there during millennium celebrations.
US officials believe he is also connected to a plan to blow up the US embassy in Sarajevo, and a plot to attack the US embassy in Paris.
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