Al-Masri, the shadowy national leader of al-Qaida in Iraq, joined al-Qaida camps in Afghanistan in the late 1990s and trained as a car bombing expert before traveling to Iraq after the U.S.-led invasion in 2003, U.S. officials said.
Al-Masri was able to step in quickly to take after al-Zarqawi, the flamboyant Jordanian-born founder of al-Qaida in Iraq, was killed in June 2006. The group launched a bombing campaign shortly afterward to show that al-Qaida was far from eliminated.
An Egyptian, al-Masri kept a lower public profile than al-Zarqawi, who appeared in militant videos including one in which he personally beheaded American Nicholas Berg.
Al-Masri's real name was Abdul-Monim al-Badawi, according to an al-Qaida statement last year describing the makeup of a new "War Cabinet."
Al-Baghdadi was the self-described leader of the al-Qaida-linked Islamic State of Iraq. U.S. military officials on Monday said his real name was Hamid Dawud Muhammad Khalil al-Zawi.
Past Iraqi claims to have captured or killed al-Baghdadi turned out to be wrong, and the Islamic State of Iraq has issued at least two denials of his capture.
Al-Baghdadi was so elusive that at times U.S. officials also have questioned whether he was a real person or merely a composite of a terrorist to give an Iraqi face to an organization led primarily by foreigners. The U.S. military once even asserted that audio recordings in the name of a fictitious al-Baghdadi were in fact read by someone else.
In the most recent message attributed to him, released near the end of March, al-Baghdadi called for continued jihad, or holy war, against Iraq's American "occupiers" in the wake of the election.