Born in Samarra, al-Baghdadi is in his early 40s. In a eulogy for bin Laden, he threatened violent retribution for his killing. Analysts regard ISIS as a greater threat now than at any time since the U.S. "surge" and the emergence of the Sunni Awakening Councils six years ago, which then turned the tide against al Qaeda in Iraq.
Reward offered by U.S. government, which lists him as Abu Du'a: up to $10 million for information leading to his location.
8. Sirajuddin Haqqani
Shifting from the Middle East to the Afghan-Pakistan border regions, several groups are positioning themselves for the exit of U.S. combat forces from Afghanistan next year. Among the most dangerous is the Haqqani Network, responsible for some of the deadly attacks in Kabul in recent years. A 2008 coordinated suicide bomb attack on the Serena Hotel in Kabul left six dead. Another strike in June 2011 killed 12 at the InterContinental Hotel.
U.S. officials say that in addition to its high-profile suicide attacks against hotels and other civilian targets in the Afghan capital, it is responsible for killing and wounding more than 1,000 U.S. soldiers in Afghanistan.
Known as Siraj, Haqqani is the son of the group's founder, and is in his early 40s.
"Siraj is a brutal criminal murderer," Gen. Jeffrey Schloesser, the outgoing commander of the U.S. 101st Airborne Division in eastern Afghanistan, told the publication Jane's in 2009.
Jeffrey Dressler, a senior analyst with the Institute for the Study of War, told CNN last year that Haqqani is "very, very competent, a very capable leader who has really grown the network over the past five, six years."
U.S. officials say the Haqqani Network is all the more dangerous in that its presence in the tribal territories of Pakistan is tolerated by the Pakistani government. The family belongs to the Zadran tribe, which spans the Afghanistan-Pakistan border and stretches to Khost province. The Haqqanis have a close relationship with both al Qaeda and the Taliban, but are also thought to have begun recruiting Chechen and Turkish jihadists.
The Obama administration designated the Haqqani Network a terror group last year. It is regarded as well-funded because of a series of legitimate and illicit businesses that stretch to the Gulf.
Reward offered by U.S. government for information leading to Haqqani's location: up to $5 million
9. Abubakar Shekau
Shekau's inclusion recognizes the growing tide of Islamist militancy in West Africa. For the last four years, he has led Boko Haram, a Salafist group in northern Nigeria that has begun cooperating with other groups as far away as Mali.
But its main focus remains churches and other Christian targets, the police and the moderate Muslim establishment in northern Nigeria. Just last month, suspected Boko Haram fighters broke into a college in Yobe state and murdered more than 40 students as they slept.
In 2010, Shekau warned that the group would attack Western interests and the following year it carried out its first suicide bombing -- against U.N. offices in the capital, Abuja -- killing at least 23 people. The group has also kidnapped and killed several Western hostages. While Bokko Haram is not an affiliate of al Qaeda, Shekau has made clear his sympathy for the group's goals. The United States made him a Specially Designated Global Terrorist in June 2012.
Two caveats here: there are conflicting reports that Shekau was killed in an August raid by Nigerian special forces. But a video that appeared weeks later purported to show he was still alive. And Boko Haram's leadership structure is opaque at best; it's unclear how much control Shekau himself exerts over its fighters.
John Campbell, a former U.S. ambassador to Nigeria, wrote last month that so far "Boko Haram has shown little interest in the world outside of Nigeria and the Sahel. But the situation in Nigeria is dynamic, and it is possible that closer ties will develop between al-Qaeda and elements of Boko Haram."
"Boko Haram" means "Western education is forbidden" and reflects the group's utter rejection of modernity and Western influences.
"Hostile to democracy, modern science, and Western education as non-Islamic, it is highly diffuse," Campbell said of the group. "For some adherents, religious, even apocalyptic, themes appear to be paramount."
Reward offered by the U.S. government: up to $7 million for his location.
10. Doku Umarov
Doku Umarov leads the Caucasus Emirate (CE), a Chechen group dedicated to bringing Islamic rule to much of southern Russia.
The U.S. State Department named Umarov a Specially Designated Global Terrorist in 2010, and said subsequently he was "encouraging followers to commit violent acts against CE's declared enemies, which include the United States as well as Israel, Russia, and the United Kingdom."
U.S. officials have been investigating whether the Tsarnaev brothers -- who were blamed for carrying out the bombing at the Boston Marathon in April -- had any links with Chechen militant groups. But nothing has surfaced connecting them with CE. And the group's main focus has been on attacking Russian institutions and civilian targets. In January 2011, it bombed Moscow's Domodedovo airport, killing 36 people, and suicide bombings of Moscow subway stations in 2010 killed 40 people.
Umarov was born in southern Chechnya in 1964, according to Chechen websites, and describes his family as part of the "intelligentsia." He came of age as the separatist campaign against Russian rule began to take root and joined the insurgency when then-Russian leader Boris Yeltsin sent troops into the region in 1994.