The key leaders are currently in Iraq and Syria where the jihadists are seeking to establish an Islamic emirate they envision as the first step toward proclaiming a new Islamic caliphate like the one that once stretched from Spain to India.
The most notorious are Abu Bakr al-Baghdadi, leader of the Islamic State of Iraq and the Levant, the new name for al-Qaida in Iraq, and Shaker Wahib al-Fahdawi, one of his field commanders.
Fahdawi is seen as the successor of the bloodthirsty founder of AQI during the U.S. occupation, the Jordanian known as Abu Musab al-Zarqawi, who unleashed a whirlwind of suicide bombings and videoed the beheadings of Western hostages then uploaded them onto the Internet.
Zarqawi was killed June 7, 2006, when a U.S. Air Force F-16 dropped two 500-pound precision-guided bombs on his safehouse north of Baghdad.
Not a lot is known about Fahdawi although Iraqi records show he was born in 1986 and studied computer science at Anbar University, until he was captured by U.S. forces in 2006 on charges of belonging to al-Qaida.
Fahdawi rose to prominence after Baghdadi, another master of mass murder, organized a string of major prison breaks in Iraq in 2012, one of which allowed Fahdawi to escape along with a number of senior jihadists from Tikrit prison north of Baghdad.
On July 2, 2013, Fahdawi was taped in broad daylight interrogating three Syrian truck drivers his group had stopped on a highway in Anbar in western Iraq near the Syrian border.
After they admitted to being Alawites, an offshoot of Shiite Islam and thus enemies of Sunni extremists, he tore off his black mask, ordered them to kneel and shot them to death.
This was all captured on video and uploaded for the world to see the new face of terror in Iraq.
A flood of photos and videos followed showing him making speeches, brazenly marching unmasked in parades, sometimes holding a falcon, sometimes automatic weapons, or making speeches. Iraqi officials say he even opened a Twitter account.
"He's the only one who kills without covering his face," Col. Yassin Dwaji, chief of police intelligence in Anbar province where Fahdawi mainly operates, told France 24.
"He's essentially a reincarnation of Zarqawi," Iraqi commentator Mushreq Abbas said.
Fahdawi was held in the U.S. military's Camp Bucca in southern Iraq where by all accounts he became a hardened extremist. In 2009 he was transferred to Tikrit where he languished until the 2012 breakout.
That was one of a series of major jailbreaks, involving large attack groups and suicide bombers, that Baghdadi organized to spring hundreds of seasoned Sunni militants to bolster his offensive against the Shiite-dominated government of Prime Minister Nouri al-Maliki in late 2013.
The Dec. 31 seizure of the Anbar cities of Fallujah and Ramadi, the provincial capital, demonstrated Baghdadi's capabilities.
Al-Qaida still holds most of these urban centers while Maliki's forces are stretched thin.
Considered utterly ruthless and highly organized, Baghdadi has been responsible for the slaughter of thousands of people, mostly but not exclusively Shiites, in hundreds of suicide and car bombings over the last five years.
Details about him are sketchy too. But his FBI rap sheet offers little beyond he's about 42, born Ibrahim Ali al-Badri in Samarrah on the Tigris River north of Baghdad.
He was arrested by the Americans in 2005 and radicalized at Camp Bucca where many al-Qaida chieftains were held, as, years later, was Fahdawi.
For reasons not known, the burly, soft-spoken Baghdadi was released in 2009. A year later he became al-Qaida chief after its two top leaders were killed. He rebuilt the organization into a deadlier force than it had ever been and pushed Iraq's death toll back up to more than 1,000 a month.
"Baghdadi is actually more capable than the man he took over from," said Iraq expert Michael Knights of the Washington Institute for Near East Policy.
"It's one of those unfortunate situations where taking out the previous leadership has made things worse, not better."