A breakaway faction calling itself Jamat-ul-Ahrar is taking responsibility for Sunday's suicide bombing
at a park in Lahore, which left at least 74 people dead and at least 362 injured.
Led by a commander named Omar Khorasani,
the splinter group is believed to have sheltered al Qaeda leader Ayman al-Zawahiri, says Michael Kugelman, the senior associate for South Asia at the Woodrow Wilson International Center for Scholars.
"They have conducted other attacks before and it seems their backs have not yet been broken despite the Pakistani military's offensive against the Pakistani Taliban in Waziristan and other tribal regions of Pakistan." said Husain Haqqani, a former Pakistani ambassador to the United States.
What is their goal?
The broader TTP probably received the most international publicity for the 2012 attack on 14-year old Malala Yousafazi
and the Peshawar school massacre
in December 2014 that left 145 dead, including 132 children.
The world was appalled by reports that gunmen were stalking the school halls, shooting children as they cowered under benches.
Formally known as the Tehreek-i-Taliban, the group has long conducted an insurgency against the Pakistani government in order to overthrow the authorities and introduce Sharia law.
"They reject the Pakistani Constitution," says Raza Rumi
, director of policy and programs at the Jinnah Institute, a Pakistani think tank. "They reject democratic process in Pakistan."
Because of Pakistan's alliances in the United States and other countries, the Pakistani Taliban also attack foreign interests in and outside of Pakistan. They are vehemently opposed to the U.S. military presence in the region.
But according to Sajjan Gohel, international security director for the Asia Pacific Foundation think tank, their interests go beyond wanting authorities to stop interfering in tribal areas.
They also have an extremist ideological agenda: "This is a terrorist outfit," he says
They seek to enforce a conservative version of Islam across the nation, and are against Western-style education for children and the employment of women.
How do they relate to other groups, including ISIS?
They are not the Taliban that U.S forces have been at war with in Afghanistan, but the adopted name is no coincidence; they have a shared heritage.
During the Soviet occupation of Afghanistan in the 1980s, fighters from Pakistan crossed over the border to fight. After returning home, they retained a close relationship with the Afghans.
The TTP at times still supports its Afghan namesake, says CNN's international diplomatic editor Nic Robertson. It offers safe haven, logistical assistance and fighters. The groups are very closely linked and share religious extremist ideology -- but the Pakistan Taliban are their own distinct group.
There are other militant groups in Pakistan's tribal region that support the Taliban that are not under the umbrella of the TTP and are not pursuing the same goal of replacing the Pakistani state with an Islamist one.
"More recently the TTP has had high-level defections to ISIS, the leaders taking their fighters with them," says Robertson. "... The TTP have brought significant firepower with them to help ISIS grow. But in this region the Taliban is still dominant."
The Pakistan Taliban are made up of disparate factions, and in recent years the group has been beset with ideological differences and internal rivalries.
Tensions first started to escalate after the group's leader, Baitullah Mehsud, was killed
in a CIA missile strike in 2009.
Hakimullah Mehsud, who replaced him, was then killed in a U.S. drone strike
in 2013, setting off a power struggle at the top of the group.
Mullah Fazlullah was appointed by a tribal council to replace Mehsud and struggled to contain the internal frictions within the group, specifically those within the Mehsud tribe.
In June 2014, the Mehsud faction announced it was parting ways with central leadership and, after attempts to convince the TTP to give up what it called "un-Islamic" practices, such as attacks in public places and kidnappings, setting up a breakaway group.
Some analysts speculated about whether the break would lead to a weakening of the group, but its activities seem only to have intensified.
After the Peshawar school attack
even the Taliban in Afghanistan, with which the TTP is closely affiliated, criticized the "deliberate killing of innocent people, women and children (as being) against Islamic principles" and expressed condolences to the attack's victims, according to spokesman Zabiullah Mujahid.
Likewise, the Afghan Taliban issued a statement Wednesday condemning the Lahore bombing, saying incidents such as this hurt other Muslims and "gave strength to the voice of infidels and security agencies."