The fall of Gadhafi in Libya gave both men the opportunity to take their operations northward into Libya from their sub-Saharan strongholds. Sources briefed by Western intelligence told CNN that Belmoktar and Abou Zeid made trips to Libya to explore the possibility of cooperation with local Libyan jihadist groups, secure weapons supplies and scout out possible locations for training facilities.
Abou Zeid made several trips to Libya in 2011, according to one source familiar with intelligence from the area.
He was one of several al-Qaida figures in North Africa who had fought in Algeria's vicious insurgency in the 1990s, when whole villages were massacred and atrocities were committed by both Islamist militants and Algeria's counterterrorism forces.
As a child growing up in a poor region of southern Algeria, Abou Zeid had little formal schooling, but his intimate knowledge of the border with Libya made him an expert smuggler.
According to Dario Cristiani, writing in the Jamestown Foundation's Militant Leadership Monitor, he was radicalized by several run-ins with the Algerian authorities. And he was at the heart of the transformation of the Algerian insurgency into an al-Qaida affiliate.
Abou Zeid's death casts further uncertainty over the fate of the French hostages his group is still believed to hold.
In December, before the French intervention in Mali, he accused the French authorities of blocking negotiations for their safe release. Several of the hostages had appeared in videos warning against military intervention for the sake of their own safety. In one video, with masked men holding AK-47s behind them, the men look exhausted and terrified.
Andrew Lebovich, a Senegal-based analyst who recently traveled to Mali, told CNN there is concern that Abou Zeid transported a number of Western hostages with him after he left Timbuktu.
If Abou Zeid was indeed killed, the expectation is his group will retaliate.
"According to available accounts, he was somebody who generated fierce respect and loyalty in his men, so unless his fighting force has been severely degraded, there's a chance his group may lash out to avenge his death in the days and weeks ahead," Lebovich said.