The meeting took place during a moonless night on a hillside on the edge of South Waziristan. Baitullah Mehsud, the self-appointed emir of the Pakistani Taliban, lay on a shawl spread over the rocky ground, sipping tea from a flask.

His face - fleshy and bearded - was visible only by the light from mobile phones and torches. Kalashnikov-wielding gunmen stood guard; a pair of local doctors crouched nearby.

Opposite him sat tribal elders from a neighbouring area, whom Mehsud had called for the meeting. He laid out his agenda, a plan to flood the area with Taliban soldiers to attack the pillars of the state - police, health workers, teachers, soldiers. "I am at war with the government," one of those present recalled him saying. The most memorable thing, one elder said later, was how ordinary Mehsud looked. "You would have difficulty picking him out of a group," he said.

That style belies one of the most feared figures in Pakistan, and now the globe. So who is Baitullah Mehsud? Ten days ago the US slapped a $5m reward on his head, elevating him, in bounty terms, to the rank of a senior al-Qaida leader.

Since February, CIA drones have concentrated their missiles on Mehsud's mountainous demesne. On Monday, he responded in the way he knows best. A gang of tribal gunmen stormed a poorly defended police training centre in Lahore, killing eight cadets. Claiming responsibility, Mehsud said the assault was in retaliation for the Predator strikes. The next attack, he threatened, would be in the heart of American power. "Not in Afghanistan, but in Washington, which will amaze the entire world," he said.

Although US General David Petraeus said he was "galvanised" by the claim, few analysts take it seriously. Where Mehsud poses a very real danger is in Pakistan. Last night a suicide bomber struck a paramilitary camp in the heart of Islamabad, killing eight Frontier Corps soldiers and injuring at least four more. The attacker struck under cover of darkness, sneaking into the camp on the side of a main road, close to a major shopping area, and blowing himself up. Two other attackers managed to flee the scene, television stations reported.

There was no claim of responsibility but early suspicions fell on Mehsud. Earlier in the day, Mehsud had claimed responsibility for a shooting at a US immigration centre in New York in which a gunman killed 13 people, saying it was revenge for American drone attacks in Pakistan. Most analysts wrote the claim off as a publicity stunt.

Few have done as much to destabilise the nuclear-armed nation of 170 million people over the past two years as this 39-year-old former gym enthusiast and border brigand. As leader of Tehrik-i-Taliban Pakistan (TTP), he controls the largest Taliban group, with influence that spans the tribal belt and extends into Swat, the tranquil tourist destination now in the hands of gunmen.

Mehsud's rise is the result of several innovations. One is suicide bombing, a tactic unheard of in Pakistan until two years ago. Last year his fighters killed an estimated 2,000 people - soldiers, police officers, suspected spies and innocent bystanders. Some were beheaded; most died in suicide blasts. The cannon fodder are young, impressionable boys and men, mostly from poor families. They are trained by Qari Hussain, Mehsud's right-hand man, who was once part of Sipa Sahaba, a murderous sectarian outfit that specialises in slaughtering Shias. Tall, imposing and generally quiet, one journalist described Hussain as "one of the most frightening people I've met".

But Mehsud's greatest achievement has been to revitalise Pakistan's jihadist network. He has brought together disparate groups of Pashtun warlords, jihadi fighters from Punjab and al-Qaida fugitives from across the Muslim world. This fusion of cash, cadres and organisation has given him the means to strike anywhere in Pakistan. Although uneducated, Mehsud is said to be focused, intelligent and quietly charismatic. "There's a sense of strength and energy about him," said Shoaib Hasan, a BBC reporter who met Mehsud in Waziristan. "And he has a charisma. When he talks, his people listen."

According to a senior Pakistani intelligence official, Mehsud was born in 1970 and spent the latter part of the 1980s fighting the Russians in Afghanistan. In the 1990s he battled alongside the Taliban militias as they swept into Kabul. He shot to prominence in 2004, filling the vacuum left by the death of Nek Muhammad, a Wazir commander killed by a US Predator drone. He exploited the Pakistan army's weakness for peace deals. A February 2005 agreement brought a halt to fighting and a donation of more than $500,000 in taxpayer money. By the time it collapsed, Mehsud had reorganised his militia, now thought to number more than 2,000 in South Waziristan alone.

In 2007 he humiliated the army by kidnapping more than 200 soldiers, who were later released in exchange for 25 Taliban prisoners - except for three Shia soldiers beheaded on video. He also strengthened ties with al-Qaida fighters. Pakistani officials said between 1,000 and 1,200 Uzbek fighters live in Waziristan, most on Mehsud turf.

But Mehsud has his rivals: Maulvi Nazir, who controls the plains and lower hills of South Waziristan, and Hafiz Gul Bahadur in North Waziristan. They are divided by turf, tribe and foreign affiliations. But since February the three have formed an alliance, the United Mujahideen Council, presumably to greet the arrival of 21,000 more US troops in Afghanistan later this year. The UMC is co-ordinated by Sirajuddin Haqqani, an Afghan warlord with strong influence in North Waziristan. Haqqani also carries a $5m US bounty on his head.

The other open question is Mehsud's links with Pakistani intelligence. For months, US officials have complained of links with the Taliban. "Mehsud is definitely an ally of some elements in the establishment," said analyst Khaled Ahmed. "And that includes the army."

Intelligence officials insist they have been pushing America to attack Mehsud. But, they argue, the root cause of the trouble is the US presence in Afghanistan. "If we settle that, what happens in the tribal areas of Pakistan will stop," said one. The other factor is the ambivalence of Pakistani public opinion towards Mehsud. Last Monday's Lahore attack may galvanise opinion against him.

Until now, Pakistanis have been prone to conspiracy theories about "foreign hands" - usually Indian, but also CIA and Mossad - in terror attacks over the past two years. Now, said Ahmed, Pakistanis are faced with the enemy in their midst. "People have not yet been associating him with terrorism so far south. This is the first time he has owned up," he said.

• An American UN worker abducted more than two months ago turned up unharmed last night, lying alongside a road in western Pakistan with his hands and feet bound. John Solecki was discovered in a village 30 miles south of Quetta, where he headed the UN refugee agency's operations.

The Taliban heartland

• The Pakistani Taliban are distinct from, but related to, the Taliban movement that ruled Afghanistan from 1996 until 2001 under Mullah Muhammad Omar. The largest group, Baitullah Mehsud's Tehrik-i-Taliban Pakistan, emerged from South Waziristan after 2005. It has seized control of a large swath of the tribal belt and part of North West Frontier province. Suicide bombings, beheadings and kidnapping are its signature tactics.

• The TTP's stated aim is to overthrow the Pakistani state, although some militants also fight in Afghanistan. The next two most important groups, led by Hafiz Gul Bahadur and Maulvi Nazir, are based along the border and focused almost exclusively on sending militants to fight in Afghanistan.

• These three groups have traditionally been rivals, but under orders from Omar they shelved their differences to form the United Mujahideen Council, which aims to counter the US troop surge ordered by US president Barack Obama.

• Meanwhile the original Taliban operates from havens in the adjoining province of Baluchistan.