Of Palestinian nationality but raised in Saudi Arabia, his true name is believed to be Zayn al-'Abidin Abu Zubadayah. He is also known as Hani and Tariq. The U.S. described him as a travel facilitator for al-Qaeda.
There is controversy if he was indeed as important as described in early reports by U.S. government spokesmen. He certainly had knowledge of al-Qaeda logistics, but the idea that he was a primary operations officer has been challenged. It is expected that the Senate will declassify some of his interrogation records in April or May 2009.
According to his Director of National Intelligence (DNI) biography, he began at a low level with al-Qaeda, as a recruiter for Arabs in Pakistan, and sending them to training in Afghanistan, Bosnia, and Chechniya. Subsequently, he became a smuggler, explosives instructor, and forger, eventually becoming director of the Khaldan training camp in Afghanistan facility by 2000. That camp, located in southeast Afghanistan near Khost, is generally agreed to have been established by bin Laden.
He also channeled funds from donors in Kuwait, Saudi Arabia, and the United Arab Emirates to al-Qaeda.
He worked with Ahmed Ressam, "an al-Qaeda member dubbed the 'Millennium Bomber' for his plot to bomb Los Angeles International Airport on New Year's Eve 1999...he was involved in discussions, after the Taliban government fell in Afghanistan, to strike back at the United States, including with attacks on American soil, according to law enforcement and military sources." He was also involved in bombing plots in Jordan.
Andy Worthington, a British author who wrote the book The Guantánamo Files: The Stories of the 774 Detainees in America’s Illegal Prison, argued that a released prisoner's account of the routine role of Khaldan argues against Abu Zubaydah having a major role in al-Qaeda. 
Later operational activity
Abu Zubaydah assisted in supporting the U.S. and Jordanian Millennium Plots. In 2001, he arranged the travel of Abu Musab al-Zarqawi, leader of Al-Qaeda in Iraq, into Iran. He was captured while arranging an attack in Israel.
There is little argument that he was committed to radical jihad, and "regarded the United States as an enemy principally because of its support of Israel...He was widely known as a kind of travel agent for those seeking such training." "It's simply wrong to suggest that Abu Zubaida wasn't intimately involved with al-Qaeda," said a U.S. counterterrorism official, speaking on the condition of anonymity because much about Abu Zubaida remains classified. "He was one of the terrorist organization's key facilitators, offered new insights into how the organization operated, provided critical information on senior al-Qaeda figures . . . and identified hundreds of al-Qaeda members. How anyone can minimize that information -- some of the best we had at the time on al-Qaeda -- is beyond me."  The fact of his involvement with travel, may have made him unusually visible before capture, perhaps through communications intelligence tracking the movements.
In his book The One Percent Doctrine, Ron Suskind quotes CIA officer Dan Coleman as saying "This guy is insane, certifiable, split personality...that's why they let him fly all over the world doing meet and greet. That's why people used his name on all sorts of calls and emails. He was like a travel agent, the guy who booked your flights. You can see from what he writes how burdened he is with all these logistics — getting families of operatives, wives and kids, out of countries. He knew very little about real operations, strategy. He was expendable, you know, the greeter..." Suskind wrote that the President, who had announced Abu Zubaydah was the chief of operations, told Director of Central Intelligence George Tenet not to let him lose face.  From the perspective of an intelligence analyst, however, if Abu Zubayhdah did not know plans, but could name a great many personalities, he could still contribute to the overall piecing-together of information. Nevertheless, it was unclear if he was making sense at all, when he spoke of targeting the Statue of Liberty and the Brooklyn Bridge. 
While he was considered of high value when captured, reports indicate he was less important than believed, and material gained through the enhanced techniques, according to the Washington Post, turned out to be useless. He did have valuable material, "chiefly names of al-Qaeda members and associates," but this was obtained before waterboarding. Prior to 9/11, he was not an official member of al-Qaeda, a "fixer" for radical Muslim ideologues,who "ended up working directly with al-Qaeda only after Sept. 11 -- and that was because the United States stood ready to invade Afghanistan." He has not been formally charged by a Military Commission.  There are competing arguments to try him for conspiracy in the U.S., or, instead, to send him to Jordan for trial there.
The argument for trying him in the U.S. centers on his links with Ahmed Ressam, who was to have led the 1999 Los Angeles attack.
Jordan, however, "tied him to terrorist plots to attack a hotel and Christian holy sites in their country..." Some U.S. officials are concerned about at trial that might set a legal precedent due to interrogation methods, and prefer a Jordanian solution.
- ICRC Report on the Treatment of 14 "High Value Detainees" in CIA Custody, International Committee of the Red Cross, February 14, 2007
- High Value Detainee Biographies, Office of the Director of National Intelligence
- Peter Finn and Joby Warrick (March 29, 2009), "Detainee's Harsh Treatment Foiled No Plots; Waterboarding, Rough Interrogation of Abu Zubaida Produced False Leads, Officials Say", Washington Post
- Andy Worthington (April 26, 2008), The Insignificance and Insanity of Abu Zubaydah: Ex-Guantánamo Prisoner Confirms FBI's Doubts
- "American Al Qaeda member Adam Gadahn tells of Jewish roots in video", Los Angeles Times, 14 June 2009
- Steven Bradbury, Office of the Principal Deputy Assistant Attorney General, Office of Legal Counsel, U.S. Department of Justice (May 10, 2005), Memorandum for John A. Rizzo, Senior Deputy General Counsel, Central Intelligence Agency, Re: Application of 18 USC 2340-2340A to Certain Techniques That May Be Used in the Interrogation of a High Value al Qaeda Detainee
- Ron Suskind (2006), The one percent doctrine: deep inside America's pursuit of its enemies since 9/11, Simon and Schuster, ISBN 0743271092, p. 100
- Suskind, p. 121