across the mountainous region and beyond into Pakistan’s settled areas and main cities.

Image Baitullah Mehsud, right, in 2004 in South Waziristan. Credit... A. Majeed/A.F.P. — Getty Images

The militant groups resisted the Pakistani military’s efforts to impose control. They sometimes cooperated in cease-fire agreements with the Pakistani military and then reneged months later. After Mr. Mehsud created Tehrik-i-Taliban, he led the group in attacks against the Pakistani state, striking military and civilian targets in various cities. The group accused the Pakistani government of siding with the United States in its war against terror, and vowed revenge for the killing of Pakistani civilians in the 2006 bombing of a madrasa in North-West Frontier Province, which was renamed Khyber-Pakhtunkhwa in 2010, and in the Red Mosque siege in Islamabad in 2007.

The United States designated the Pakistani Taliban a terrorist organization in September 2010 and placed a $5 million reward for information leading to the arrest of their leader, Hakimullah Mehsud.

Q. Who is Hakimullah Mehsud, and what does his death mean for the Pakistani Taliban?

A. Mr. Mehsud became the leader of the Pakistani Taliban after an American drone strike killed Baitullah Mehsud in August 2009. A onetime driver for the Taliban who had risen to prominence through a series of daring attacks, he played a major role in the humiliating kidnapping of 250 Pakistani soldiers in 2007. He later stole American jeeps as they were being transported to Afghanistan and was filmed driving around in one.

Mr. Mehsud proved a wayward, vicious leader. He appeared at the execution of a former Pakistani intelligence officer, Sultan Amir, known as Colonel Imam, in 2011. Colonel Imam had long been a trainer and mentor to the Taliban in Afghanistan and Pakistan, yet Mr. Mehsud ignored efforts to intercede on his behalf by senior Taliban figures, including Mullah Mohammad Omar, the Afghan Taliban leader, and Sirajuddin Haqqani, the leader of the powerful Haqqani network.

Hunted by American drones, Mr. Mehsud adopted a low profile in recent months and was rarely seen in the news media. But in a BBC interview that was broadcast in October, he vowed to continue his campaign of violence. He was aware that the C.I.A. was seeking to kill him, he said, adding: “Don’t be afraid. We all have to die someday.”