(CNN) -- Abu Yahya al-Libi, al Qaeda's No. 2 man, was killed in Pakistan on Monday, according to U.S. officials. 

Al-Libi's death was "another serious blow to core al Qaeda," White House spokesman Jay Carney said. 

Al-Libi, 49, was a well-regarded figure in jihadist circles and had emerged as one of the terrorist network's most important clerics and propagandists, appearing in countless videos in recent years. 

He was killed by a CIA drone strike, according to U.S. officials. Drone strikes remain a highly contentious issue between the United States and Pakistan. 

Who is Abu Yahya al-Libi? 

By most accounts, al-Libi was effectively al Qaeda's deputy leader. 

A Libyan citizen and an Islamic scholar, al-Libi bolstered his credibility within jihad groups after escaping from U.S. custody in Afghanistan in 2005. 

He became the public face of al Qaeda and used his religious training to justify the organization's actions. As one of the group's chief ideologues and propagandists, al-Libi appeared in numerous recruitment videos in which he cast himself as a sheikh with the legitimacy to issue fatwas. 

Other than his appearances in propaganda videos, it's unclear which plots against the West al-Libi was involved in. A wanted ad from the U.S. State Department described him as a "key motivator in the global jihadi movement," and said that "his messages convey a clear threat to U.S. persons or property worldwide." 

What does his death mean for al Qaeda? 

This is a "very serious blow" to al Qaeda, according to Noman Benotman, a former senior member of the Libyan Islamic Fighting Group who spent significant time with al-Libi in the 1990s. No one else within the group rivals his legitimacy as a religious scholar nor has the credibility in the Arab world to provide Islamic justifications for al Qaeda's global campaign of terrorism, he said. 
HOW WAS HE KILLED?
killed by a CIA drone strike