Four of these leaders -- Saif al-Adel, Mahfouz Ould Walid, Ilyas Kashmiri and Adnan al-Shukrijuma -- are reported to be in the North Waziristan region of Pakistan, plotting new attacks and recruiting operatives for special operations.
Adel, a veteran al-Qaida chieftain and former colonel in the Egyptian army's Special Forces, moved to Waziristan in 2010 from Iran, where he had been apparently restricted since 2002.
A close associate of Khalid Sheik Mohammed, alleged mastermind of 9/11, Adel, a 50-year-old Egyptian, is one of al-Qaida's senior strategists who sat on its military committee.
He has been linked to the Oct. 12, 2000, bombing of the USS Cole in Aden harbor that killed 17 sailors, and to the U.S. embassy bombings in East Africa Aug. 7, 1998, that killed more than 200 people.
Adel -- real name Muhammad Ibrahim Makkawi -- has a $5 million U.S. bounty on his head and is wanted in the United States for allegedly training the 9/11 suicide attackers.
Ould Walid, aka Abu Hafs the Mauritanian, is a veteran jihadist who fought the Soviets in Afghanistan in 1979-89.
Aged 36, he was a close adviser to Osama bin Laden before they became separated during the U.S. invasion of Afghanistan following 9/11. He accompanied al-Adel from Iran.
Arab intelligence sources say that the hard-line clerics and senior Revolutionary Guards officers who oversaw Abu Hafs and al-Adel during their sojourn in Iran allowed them to operate with considerable freedom and have access to sophisticated electronic communications systems.
The Americans mistakenly reported in January 2002 that Abu Hafs, a key military planner in the al-Qaida hierarchy, had been killed in Afghanistan.
Saudi-born Adnan Shukrijuma, 35, is one of the few al-Qaida leadership cadre who has actually lived in the United States. That makes him a key figure in the reported efforts to plan attacks inside the United States.
He is a naturalized U.S. citizen. His family moved to Florida in 1985 where he studied computer engineering and started moving in Islamist circles before going underground following 9/11.
He has a $5 million U.S. bounty on his head but has eluded a global manhunt for a decade. Al-Qaida leader Abu Zubaydah, captured in Pakistan March 28, 2002, told CIA interrogators of several al-Qaida plots.
One involved "Jaafar the pilot" -- Shukrijuma in one of his many disguises -- who he said would deliver an "American Hiroshima" using radioactive bombs.
But it wasn't until Khalid Sheik Mohammed, who was captured in Rawalpindi, Pakistan, March 1, 2003, spilled the beans about the elusive Shukrijuma that the Americans realized he had lived right under their noses in Fort Lauderdale for years.
U.S. authorities say he was the mastermind behind a failed attack on the New York subway. The Long War Journal Web site, which monitors global terrorism, calls him al-Qaida's "chief of operations for North America."
Ilyas Kashmiri, a 45-year-old Pakistani, heads al-Qaida's Lashkar al Zil, or Shadow Army, an elite jihadist unit of seasoned fighters made up of Arabs, Central Asians and Pakistanis.
He was linked to David Coleman Headley, an American arrested for involvement in the November 2008 carnage in the Indian city of Mumbai in which 160 people were killed.
Headley also has been charged with conspiring to attack Jyllands-Posten, a Danish newspaper that incensed jihadists by publishing cartoons of the Prophet Mohammed in 2005.
Kashmiri's operational signature is attacks by groups of highly trained gunmen as in Mumbai. He has threatened similar attacks in the West.
In a 2009 interview, Kashmiri said Mumbai "was nothing compared to what has been planned for the future."
According to Islamist sources, he joined the Pakistani-directed insurgency against India over divided Kashmir in his teens. By 1991, he was a key figure in Harkat-ul Jihad-i-Islami, one of the most ferocious of the Pakistani groups active in Kashmir.
He joined bin Laden in 2005 and is considered one of his most effective commanders and planners.
Kashmiri, who sports a red henna-dyed beard, is virtually unknown outside the intelligence community. But he's rated as a most dangerous adversary, deadly, highly innovative, bold and hard to track.