The Taliban commander believed responsible for at least two ferocious attacks in Kabul over the last few weeks knows the Afghan capital very well. Five years ago, Mullah Sheerin Akhond, as he is called, spent long months walking the streets incognito, and as he learned the lay of the land, he also honed his hatred for the people there.

“He is a very nasty character,” one knowledgeable Afghan Taliban source tells The Daily Beast. “His Islamic scholarship is nil, but he has a harsh, fanatical attitude about anyone who lives in areas controlled by the Afghan government. In his view, it is permissible to kill anyone who lives in Kabul because they are supporting the Afghan government.”

And members of that government agree: Mullah Sheerin is a very nasty character indeed. “At the moment, when it comes to atrocities targeting civilians, he is the most cruel and inhuman of the Taliban,” says a senior aide to Afghan President Ashraf Ghani, who asked not to be named because he doesn’t have permission to speak on the record.

There had been hope that when the Pakistani military turned on the old Haqqani Network, pushing it out of the havens it had enjoyed for 40 years in North Waziristan, attacks in nearby Kabul would diminish. But Mullah Sheerin quickly stepped in—and with a vengeance. “Haqqani would use kilograms of explosives,” as one Western diplomat put it, “but Mullah Sheerin uses tons.”

The recent attacks bear that out, although they hardly appear to have been random and they are not always claimed. On Aug. 25, gunmen attacked the American University of Afghanistan, leaving more than a dozen people dead, and dozens more wounded.

Then, on Monday of this week a massive car bomb blew up on a bustling street near the Ministry of Defense. As rescue workers arrived at the scene, another huge suicide bomb detonated. At least 24 people reportedly were killed, some of them senior security officials, and more than 90 were wounded. Gunmen followed up the attack, barricading themselves inside a building and skirmishing with authorities throughout the night.

To make matters worse, there appears to be competition between the Taliban and the partisans of the so-called Islamic State to see who can inflict the worst carnage. In July, ISIS targeted a street demonstration and slaughtered more than 80 people.

One Taliban official says privately that he’s very uncomfortable with Mullah Sheerin and his tactics, which are likely to inspire hatred, not support. “Some Taliban do not like him,” says this official, “but he is too strong to be disputed.”

Mullah Sheerin Akhond, at age 45, is now head of the Taliban military council for northeast Afghanistan and Kabul, and some diplomats say they believe he is also the head of the Taliban intelligence committee. His core strategy appears to be to undermine confidence in the government’s ability to protect the people, and with some success.

He is no stranger to the Western and Afghan intelligence services that have been watching him for years.

Although Mullah Sheerin kept a low profile in the past, he was known to be very close to the late founder and leader of the Taliban, the one-eyed Mullah Omar.

Another Afghan Taliban commander contacted by The Daily Beast, Mullah Salih Khan in Helmand province, tells us, “I knew Mullah Sheerin from day one. He is a very devoted Taliban commander, and has a very sharp mind, with a genius for security,” whether providing it, or thwarting it.

The role he played for Mullah Omar was head of security. “Sheerin used to wake up early in the morning and go to sleep only after Mullah Omar slept,” says Mullah Salih Khan. “He was one of Mullah Omar’s most trusted men.”

According to Mullah Salih, Sheerin “was giving military instructions to top Taliban commanders from Mullah Omar’s office, conveyed as if they were Mullah Omar’s directions. In fact they were Mullah Sheerin’s ideas.”

Afghan intelligence officials believe that, like the Haqqani network before him, Mullah Sheerin has close ties to Pakistan’s Inter-Services Intelligence agency, or ISI.

Rahmatullah Nabil, who served until recently with the Afghan intelligence service, NDS, says Mullah Sheerin “is not just behind recent attacks, he was behind several other barbaric attacks in Kabul.” Nabi mentioned the attacks on the night of Aug. 7 when one bomb exploded near a police academy and another near an army base, killing at least 35 people and wounding hundreds more.

Nabi claims that Mullah Sheerin is “very close to the ISI” and to Seraj U Din Haqqani, also known as khalifah, or the caliph. According to Nabi, Mullah Sheerin is living in Peshawar, where even his security guards are provided by the ISI. “Pakistan never took action against him,” Nabi told The Daily Beast.

Pakistani officials, as usual, reject such allegations out of hand.