Mullah Abdul Ghani Baradar, the Taliban's No. 2 captured in Pakistan last week, was a charismatic military strategist who helped rebuild the group into a powerful guerrilla force after the U.S.-led invasion of Afghanistan.
A hard-liner, he rejects a political role for the Taliban, and inspires many others to do the same. But former associates say he is one of the group's few senior figures with the influence to start a dialogue, in the unlikely event he so wished.
Most people only know of one Taliban leader, the one-eyed reclusive Mullah Mohammad Omar, who protected al Qaeda leader Osama bin Laden.
But it was Baradar who was actually running the daily Taliban show, securing finances, planning military campaigns and studying the latest U.S. policy statements on plans to weaken his fighters and stabilize Afghanistan.
Mullah Baradar, captured in Karachi in a joint U.S.-Pakistani operation, is described as the Taliban's top strategist, pioneer of commando-style raids and an advocate of suicide bombings.
He is the man who most likely fired up militants to combat one of the biggest NATO offensives in Afghanistan, now underway in Helmand Province.
Baradar, born in 1968, was the right-hand man to Mullah Omar, who gave him the nickname Baradar (brother), a move that provided great clout and prestige in Taliban circles.
Like Mullah Omar, he became battle-hardened fighting Soviet occupation troops in the 1980s, and like many Taliban members, his education was deeply rooted in Islam.
He emerged as a brilliant commander, responsible for developing military strategies for a group with a complex relationship with al Qaeda that led to its fall from power in Kabul after the 2001 American-led invasion.
In the difficult times that followed, Mullah Baradar gained other skills as well, serving as a deputy to Mullah Omar on political affairs. But he never sought the limelight, preferring instead to quietly gain the trust of the Taliban leader.
Even his beard, former Taliban officials say, is low profile compared to the traditionally long and thick ones sported by Taliban commanders and fighters.
In recent years, Omar conveyed all his military and political messages to field commanders in Afghanistan through Mullah Baradar, Taliban officials say.
That could provide the Americans and Pakistanis with high-value information, something in huge demand since a double agent suicide bomber killed seven CIA employees at a U.S. base in eastern Afghanistan in December.
But by most accounts, he is not the kind of man who will play ball. Judging by comments he made to Newsweek magazine last year, Mullah Baradar's philosophy is simple -- fight until every foreign soldier is expelled from Afghanistan.
A Taliban official said that unlike other Afghan Taliban leaders, Mullah Baradar did not enjoy good relations with Pakistan, a powerful regional player with strategic ties to some militant groups fighting Western forces in Afghanistan.
That may have led to his downfall.
In something very rare in the austere Taliban leadership culture, Mullah Omar and Mullah Baradar were known to crack jokes in front of comrades.
One day they even challenged each other to a traditional Afghan contact sport -- each man holds one of his ankles behind his back and tries to knock down the other by hopping into him, a former Taliban official said.
Mullah Omar won that after securing a higher bit of ground to lunge from.
(Writing by Michael Georgy; Editing by Bryson Hull and Raju Gopalakrishnan)