Now facing the worst unrest since the revolution, Gaddafi's moves are as opaque as ever. Amid feverish speculation about the future, everything he has ever done suggests he will not relinquish power voluntarily. "We will all die on Libyan soil," sources close to his family told the Saudi paper al-Sharq al-Awsat.

According to unconfirmed reports the repression in Benghazi in eastern Libya is being led by his son Khamis, the Russian-trained commander of an elite special forces unit. Another son, Saadi, is there too, with Abdullah al-Senussi, veteran head of military intelligence.

Last Friday Gaddafi appeared briefly in central Tripoli to cheers from supporters but has not spoken in public or left the heavily-guarded Bab al-Aziziya barracks in the centre of the capital – the target of a US bombing raid in 1986.

The crushing of protests in Benghazi and elsewhere bears the hallmark of his instinctive brutality when faced with challenges to his rule, analysts say.

In the 1980s he sent hit squads to murder exiled "stray dogs" who challenged the revolution. Islamist rebels at home were crushed in the 1990s and in 1996 1,000 prisoners were gunned down in an infamous prison massacre.

"For Gaddafi it's kill or be killed," said opposition writer Ashour Shamis. "Now he's gone straight for the kill."

The uprisings in neighbouring countries do not appear to have shaken his resolve to stay in power. He sent messages of support to Tunisia's Zine al-Abdine Ben Ali and to Egypt's Hosni Mubarak before they stepped down.

Regime survival has marked Gaddafi's moves in recent years – from the handover of the Lockerbie bombing suspects to the surrender of his WMD programme after the invasion of Iraq in 2003. No-one expects him to give up peacefully. He may make gestures such as promising closer consultation or boosting investment in housing and social services, but that seems unlikely to satisfy protesters after such brutality towards ordinary Libyans.

"Gaddafi will find it hard to make concessions in order to survive," said Sir Richard Dalton, a former British ambassador to Libya. "The attitude of the regime is that it's all or nothing."

Another key question is whether the condemnation of western friends will have any effect. Libya's warning to the EU that it will halt cooperation over illegal immigration suggests it will not.

Power in Libya is devolved in some areas to popular committees and there is sometimes talk of dramatic restructuring of government. But all key policy areas – defence, foreign affairs, and security – are firmly in Gaddafi's hands.

Like Mubarak, the Libyan leader has no designated successor. Gaddafi's advice is likely to be coming from his son Muatassim, his national security adviser and leading contender to succeed him. Two years ago Muatassim tried to set up another special unit to rival the one commanded by Khamis.

In recent months both have seemed more powerful than another brother, the reformist Saif al-Islam. Saif focused on civil society and political and economic reform but has taken a back seat in the face of opposition from the old guard and the revolutionary committees. "Creating the appearance of useful employment for Gaddafi's offspring has been an important objective for the regime," reported the US ambassador in a cable released by WikiLeaks.

Other sons have embarrassed their father. Saadi is notoriously ill-behaved, with a record of scuffles with police in Europe, abuse of drugs and alcohol. Hannibal's misbehaviour in Geneva caused a long rupture in Swiss-Libyan relations.

"Gaddafi is a complicated individual who has managed to stay in power for 40 years through a skilful balancing of interests and realpolitik methods," commented the former US ambassador Gene Cretz. Libya's current crisis looks like Gaddafi's biggest challenge yet.