Any compilation of the world's most dangerous terrorists is a hazardous undertaking, a shifting list that's open to endless debate.
If you live in Moscow, Chechen Islamist leader Doku Umarov would feature prominently. Many Israelis would likely include Hezbollah leader Hassan Nasrallah on their list and people living in the southern Philippines, the Abu Sayyaf group.
Some terror figures who were among the most wanted several years ago, such as Abu Anas al Libi -- who was captured last weekend in Libya -- appear not to have been active for some time. Even some terrorists try to retire. The last list compiled by CNN included senior al Qaeda operative Saif al Adel. He has vanished from the radar and may have been under house arrest in Iran.
Other figures lose relevance as their group loses territory, membership and/or funding. Groups such as al Qaeda in the Islamic Maghreb have been prone to internal rifts. Additionally, al Qaeda, especially in Pakistan, has moved away from identifying senior operational figures because of the effects of U.S. drone strikes, so some of a new generation of most dangerous terrorist figures may not yet be known to us.
The following selection is intended neither as definitive nor a "league table." It focuses not on organizations but on men (and they are all men) alleged to be plotting, directing -- and in some instances carrying out -- acts of terror aimed at causing mass casualties among civilians.
Some are ideologues and planners, others "operational," and some are both. They think and act in a regional and in some cases a global context. Some of the individuals below have appeared on previous lists compiled by CNN and others, and have lived long enough to warrant a second or third appearance.
Others are only now making a name for themselves among the world's counterterrorism agencies, as they take advantage of conflict or the collapse of state authority, forge new alliances or develop new ways of bringing terror to the international stage.
Despite the whittling away by drone attacks of "al Qaeda central" in the mountainous border region between Afghanistan and Pakistan, the group's leader remains vocal and active in trying to harness the disparate affiliates that claim the al Qaeda name.
Since former leader Osama bin Laden's death in 2011, al-Zawahiri has sought to take advantage of the unrest sweeping the Arab world, and has recognized that groups such as al Qaeda in the Arabian Peninsula (AQAP) and al Qaeda in the Islamic Maghreb are better placed to carry out attacks than the ever-diminishing core that remains in "Af-Pak." At times, al-Zawahiri has struggled to exercise authority over groups such as the Islamic State in Iraq, not least because of the difficulty in communicating with far-flung offshoots.
Aware that pulling off another 9/11 is a remote possibility, al-Zawahiri has suggested a shift to less ambitious and less expensive but highly disruptive attacks on "soft" targets, as well as hostage-taking. In an audio message in August he recommended taking "the citizens of the countries that are participating in the invasion of Muslim countries as hostages."
Al-Zawahiri, an Egyptian doctor who is now 62, is not the inspirational figure to jihadists that bin Laden was, but he is trying to fashion a role as the CEO of a sprawling enterprise. According to the Economist, he may be succeeding. "From Somalia to Syria, al-Qaeda franchises and jihadist fellow travellers now control more territory, and can call on more fighters, than at any time since Osama bin Laden created the organisation 25 years ago," it wrote this month.
Reward offered by the U.S. government for his capture: up to $25 million
2. Nasir al Wuhayshi
For someone thought to be about 36 years old, Wuhayshi's terror resume is already extensive. Once bin Laden's private secretary in Afghanistan, he returned to his native Yemen and ended up in jail. But not for long: He and several other al Qaeda operatives dug their way out in 2006. He went on to to help found al Qaeda in Yemen, and began launching attacks on Yemeni security services and foreign tourists, as well as directing an ambitious attack against the U.S. Embassy in Yemen.
He is now the emir of AQAP, widely regarded as the most dangerous and active of al Qaeda's many offshoots. A slight figure with an impish sense of humor, according to some who have met him, Wuhayshi appears to have been anointed al Qaeda's overall deputy leader in a bold move by al-Zawahiri to leverage the capabilities of AQAP. Seth Jones, a Rand Corporation analyst, called the appointment "unprecedented because he's living in Yemen, he's not living in Pakistan."
If al-Zawahiri is al Qaeda's CEO, Wuhayshi appears to be its COO -- with responsibilities that extend far beyond Yemen. It appears that in 2012 he was already giving operational advice to al Qaeda's affiliate in North Africa.
Despite a concerted effort by the Yemeni government and the United States to behead AQAP, Wuhayshi survives, and his fighters have recently gone on the offensive again in southern Yemen. The group is bent on exporting terror to the West -- both through bomb plots and by dispatching Western converts home to sow carnage.
3. Ibrahim al-Asiri
Not a household name, but one that provokes plenty of anxiety among Western intelligence agencies. Al-Asiri, a 31-year-old Saudi, is AQAP's master bomb-maker, as expert as he is ruthless. He is widely thought to have designed the "underwear" bomb that nearly brought down a U.S. airliner over Detroit on Christmas Day 2009, as well as the ingenious printer bombs sent as freight from Sanaa, Yemen, and destined for the United States before being intercepted thanks to a Saudi tip-off. The bombs were so well hidden that at first British police were unable to find one device even after isolating the printer.
Al-Asiri also fitted his younger brother Abduillah with a bomb hidden in his rectum in an effort to kill Saudi Arabia's counter-terrorism chief, Mohammed bin Nayef. The brother died in the attack; bin Nayef survived.
His trademark explosive is PETN -- a white, odorless powder than cannot be detected by most X-ray machines.
Al-Asiri is thought to be somewhere in the vast mountainous interior of southern Yemen. The anxiety among Saudi and Western intelligence officials is that he has passed on his expertise to apprentices.
4. Ahmed Abdi Godane
Godane, aka Mukhtar Abu Zubayr, became the leader of the Somali group Al-Shabaab at the end of 2008. Traditionally, Al-Shabaab has been focused on bringing Islamic rule to Somalia, and as such has attracted dozens of ethnic Somalis (and a few Western coverts) from the United States and Europe. But Godane appears to be refocusing the group on terrorist attacks beyond Somalia, against the east African states that are supporting the Somali government -- especially Uganda and Kenya -- and against Western interests in east Africa.
The Westgate Mall attack in Nairobi September 21 was Al-Shabaab's most audacious, but not its first nor most deadly outside Somalia. In 2010, Al-Shabaab carried out suicide bombings in the Ugandan capital, Kampala, in which more than 70 people were killed. But the Westgate siege, which left 67 people dead, demonstrated Godane's desire to align his group more closely with al Qaeda. In a taped message afterward, he noted the attack took place "just 10 days after the anniversary date of the blessed 9/11 operations."