Interviews with former military officials and government officials, local residents and a former Taliban member who worked in proximity to Mr. Mehsud’s inner circle portrayed him as a militant leader who is barely educated, attracts more knowledgeable people to his side and is ruthless in his goal of an extreme form of Islamic rule.

He and his main ally, Qari Hussain, whom officials and associates have described as a highly trained and vicious militant, have methodically built up strongholds in North and South Waziristan  killing uncooperative tribal leaders, recruiting unemployed young men to their jihad and filling the vacuum left by a lack of government services. Now, they also have lieutenants and allies across the tribal region.

In South Waziristan, they run training camps for suicide bombers, some of them children, according to the former Taliban member. Their realm is so secure that in April Mr. Mehsud’s umbrella group, Tehrik-e-Taliban Pakistan, held a conference of thousands of fighters that culminated in a public execution, according to a local resident.

Local Pakistani authorities say they are helpless to deal with Mr. Mehsud’s group. In a measure of their despair, on Wednesday the authorities in the Mohmand district, where the conference and public execution were held, announced a truce with the Taliban.

Mr. Mehsud was once a minor figure in the small Shabikhel branch of the fierce Mehsud tribe that lives in South Waziristan, whose inhospitable territory remained a sliver of imperial India left unconquered by the British.

But he managed to enhance his stature through the ambivalence  or protection, according to some officials  of the Pakistani authorities, say former Pakistani military officials and tribal leaders. His strength grew quickly after February 2005, when the military, then under the control of President Pervez Musharraf, signed a peace deal with him.

“That was when I knew the army was not serious,” said a tribal leader who has dealt with Mr. Mehsud and would not be named for safety reasons. “If the army took firm action they could crush him in two months.”