With a $10 million bounty on his head, Abu Musab al-Zarqawi (search) is one of the most hotly sought Islamic extremist leaders with links to Al Qaeda.
The Jordanian is suspected of planning some of the worst terror bombings in Iraq and is believed to have written a captured document sent to Al Qaeda commanders outlining a campaign to foment civil war between Iraq's Sunni and Shiite Muslims.
He was linked to deadly bombings last year in Turkey and Morocco and accused of orchestrating the 2002 assassination of a U.S. diplomat in Jordan. And Britain tied him to a foiled ricin poisoning plot.
Little evidence has been presented, though, so it is not clear how firm the allegations are.
A prominent Sunni cleric in Iraq, Hareth al-Darri, called al-Zarqawi "an imaginary character" Wednesday and said he doubted the Jordanian had much of a role in the insurgency.
Jordanian officials describe al-Zarqawi as a religious zealot who is determined to cleanse Islamic countries of sinful Western morals and say he is known for eloquent preaching about the Muslim holy book, the Quran (search).
Asked if al-Zarqawi was behind homicide bombings that killed 100 Iraqis on Tuesday and Wednesday, Maj. Gen. Charles H. Swannack Jr., commander of the 82nd Airborne Division, said that based on the captured letter, there appeared to be a relationship.
However, an American official in Washington, speaking on condition of anonymity, said it was possible al-Zarqawi was involved in the bombings but said they were more likely staged by Saddam Hussein loyalists.
This week's bombings aside, U.S. authorities said previously that evidence was mounting to suggest al-Zarqawi had a hand in deadly attacks at a Shiite mosque in Najaf, the U.N. offices in Baghdad and an Italian paramilitary police post in Nasiriyah.
The official in Washington declined to discuss where al-Zarqawi ranks among wanted terror suspects, but added: "Would U.S. forces like to get their hands on Zarqawi? You bet."
In Iraq, Col. Ralph Baker of the 1st Armored Division said this week's bombings resembled "the operating technique" of Al Qaeda or Ansar al-Islam (search), a radical Muslim group based in Iraq's Kurdish region that is affiliated with Usama bin Laden's network. Officials in Washington, Jordan and other countries have said al-Zarqawi has strong ties to Ansar.
After the U.S.-led war that ousted the Taliban regime in Afghanistan two years ago, Washington described al-Zarqawi as one of eight Al Qaeda operations chiefs and listed him among about two dozen of the most-wanted fugitives.
Last year, Secretary of State Colin Powell used al-Zarqawi as an example of Al Qaeda ties to Saddam's regime, saying al-Zarqawi received hospital treatment in Baghdad after fleeing Afghanistan. Intelligence sources said he apparently was fitted with an artificial leg.
U.S. intelligence officials also said then that al-Zarqawi considered himself and his followers to be operating independently of Al Qaeda's chain of command. But they said he relied on Al Qaeda for money and logistical support.
Al-Zarqawi, 37, was born Ahmad Fadeel Nazzal al-Khalayleh, but uses a nom de guerre derived in part from the name of his hometown in Jordan, Zarqa. Now believed to be hiding in Iraq, he has been involved with Islamic militant groups since going to Afghanistan in the late 1980s to help fight the occupying Soviet army.
According to his family, he returned to Zarqa, an industrial town 17 miles from the Jordanian capital, Amman, in 1992. The family, which belongs to the Bedouin tribe Bani Hassan, says he married but couldn't find work.
His mother, Um Sayel, last year described her youngest son as a modest man and devout Muslim and said he was wrongly being accused of terrorist activities. "My son is a good man, an ordinary man, a victim of injustice," she said.
Um Sayel, who uses her eldest son's name for identification, wouldn't talk about al-Zarqawi's 1992-97 stint in prison. Jordanian security officials say he was jailed for working with groups that wanted to overthrow the monarchy and set up an Islamic state and also plotted to attack foreigners in Jordan.
Al-Zarqawi fled Jordan in 1999, shortly before authorities announced they had foiled a gas attack on American and Israeli tourists during millennium festivities and charged him with planning the assault. Jordanian officials say he went to Afghanistan, where they say he showed a talent for making poison gas and developed close contacts with bin Laden.
He reportedly left Afghanistan as the Taliban regime collapsed two years ago, apparently having been wounded during the U.S. bombing or in fighting with Washington's Afghan allies. U.S. authorities say he stayed in Iran for a time, then spent two months in Baghad receiving medical care.
Intelligence officials in several countries say al-Zarqawi has been on the move ever since, forging new terrorist cells and planning attacks.
A little over a year ago, Jordanian authorities named al-Zarqawi as the mastermind behind the October 2002 murder of Laurence Foley, a 60-year-old administrator of U.S. aid programs in Jordan.
In a German court last year, Shadi Abdellah, a Palestinian on trial for allegedly plotting to attack Berlin's Jewish Museum and a Jewish-owned disco, testified he was working for al-Zarqawi. He said they met in Afghanistan.
German authorities have reportedly said they believe al-Zarqawi was appointed by Al Qaeda's leadership to arrange attacks in Europe.
Moroccan government sources said a group blamed for bombings last May that killed 45 people in Casablanca got its orders from al-Zarqawi. In Turkey, officials said he was believed to have played a role in bombings that killed 63 at two synagogues, the British consulate and a British bank in Istanbul in November.