He is slim with an olive complexion. His name, it is thought, is Saif al-Adel. He is, according to one of his former associates, "a certifiable psychopath.'
Adel, the most senior al-Qaeda operative still at large after Osama bin Laden and his closest associate, Ayman al-Zawahiri, is America's prime suspect for the bomb attacks in Riyadh 12 days ago.
US intelligence operatives are focusing their hunt on the 40-year-old Egyptian-born militant, who they claim is operating from Iran.
After recent successes in capturing senior al-Qaeda figures in Pakistan, they are confident Adel, also known as Mohammed Makkawi, will soon be brought to justice.
The Americans say Adel has been linked to the attacks in Riyadh, which involved three almost simultaneous suicide attacks, by intercepts of communications between conspirators. Although almost all those involved in the cell were Saudis, including their local commander, the Americans believe they took orders from more senior figures out of the kingdom. The most likely such figure, they believe, is Adel. And his most likely location, they say, is Iran.
"There's no question but that there have been, and today, senior al-Qaeda leaders [are] in Iran -- and they are busy," Donald Rumsfeld, the US defense secretary, told reporters last week. The Pentagon is now explicitly committed to a policy of "regime change" in Iran involving the transmission of anti-government broadcasts and possible support for the Iraq-based armed opposition group, the Mujahidin-e Khalq. In an echo of rows over Iraq, the new hardline stance is opposed by the US State Department and the British Foreign Office. As with Iraq, linking Iran to al-Qaeda is a key element of the hawks' strategy.
"They are teeing things up for more military activity. Iran has been named as part of the axis of evil and there are many in America who want to deal with any perceived threat with force," said Dilip Hiro, an author and expert on Iran.
However, evidence points to a more complex picture. In the aftermath of the American attack in Afghanistan several hundred Islamic militants, some of whom were linked to al-Qaeda, fled into south-east Iran. Some were picked up by the authorities, others appear to have been sheltered by hardline groups acting contrary to orders from Tehran; some were able to hide out with well-armed desert tribes in the remote and arid border areas.
Intelligence dossiers obtained by The Observer News Service in Iraq earlier this year revealed that scores of militants made their way across Iran from Afghanistan to join the hardline Ansar-ul-Islam group, which had occupied an enclave in the north-east of Iraq, in the spring and summer of last year. The Ansar group was destroyed by a joint Kurdish and US operation in March. It is unclear whether Adel, a former colonel in the Egyptian special forces, made his way to Iran, although it is widely accepted that he escaped the war in Afghanistan unscathed.
Adel fought against the Soviet Union in Afghanistan during the late 1980s and was one of a small number of hardened militants who, some time between 1989 and 1992, were assigned from the Egyptian Islamic Jihad group to Osama bin Laden's newly formed al-Qaeda.
After several years in Sudan, and a short period training militants in Somalia, he returned to Afghanistan with bin Laden in 1996. He has been indicted by the US for his role in both the bombing of US embassies in East Africa in 1998 and the attack on the USS Cole in Yemen in October 2000.