The AUC is in conflict with the FARC - the country's largest guerrilla force

But more accurately the AUC has its roots in the paramilitary armies built up by drug lords, most notably Jose Rodriguez Gacha of the Medellin cartel, and the AUC present leader's brother, Fidel Castano.

As the drug lords became landowners, buying up vast tracts of Colombia - some 3.5 million hectares of agricultural land - they took over local self-defence groups and set up their own, to protect not the local population but their own interests.

And as big landowners, they found themselves facing kidnapping and extortion by the country's Marxist guerrillas.

Carlos Castano

So when the Revolutionary Armed Forces of Colombia (FARC) kidnapped the father of Fidel and Carlos Castano and then murdered him, the family swore revenge.

They have been taking it ever since, killing thousands of guerrillas and suspected rebels sympathisers.

The AUC counts about 9,000 members

Carlos Castano is the present head of the AUC - although officially, since May 2001, just its political head.

He inherited his position from his elder brother Fidel, killed in a guerrilla ambush 1994.

Carlos has built up the paramilitary force of 300 he inherited from his brother to an army of some 9,000 today.

In 1997, he formed the AUC as an umbrella group under which all were welcome: local warlords, drugs traffickers and disaffected members of the security forces - in short anyone prepared to kill guerrillas.

Paramilitary boom

One of the main developments in the administration of President Andres Pastrana has been the explosive growth of the paramilitaries.

The AUC has grown in strength and influence - due to links with the army and financing by business interests and landowners tired of guerrilla extortion.

The failure of President Pastrana's peace process, the intransigence of the guerrillas and their abuse of government concessions have all fed the paramilitary coffers as Colombians see the state unable to defend them.

The number of paramilitaries has grown under Andres Pastrana

With this rise has come an increase in massacres, and the murders of left-wing intellectuals, union workers, human rights activists and journalists, as the right-wing death squads seek to silence all those that speak out against them, or in favour of the guerrillas.

Working on the principle that draining the water will kill the fish, the paramilitaries have provoked massive displacement through their policy of massacres and terror.

The locations may change, but the operating procedure remains the same.

The death squads arrive in communities in areas of guerrilla influence with a list in hand. The list contains names of suspected guerrilla sympathisers.

All those on the list are killed, usually in front of their families and in a most gruesome manner. The message is brutally simple: support the guerrillas and you will die.

And it has had great effect in many parts of the country, "cleansing" them of guerrilla presence.

But those that flee run into the arms of the rebels and Colombia's polarisation increases.

Army links

Like the guerrillas, the paramilitaries earn much of the money from drugs trafficking but, unlike the guerrillas, their history has been inextricably linked to drug barons across the country, which is still true today.

There is an undeniable body of evidence that shows co-operation between army units and paramilitaries.

The Colombian Government has worked hard to sever links between the military and the paramilitary death squads but these still exist and indeed groups like Human Rights Watch insist the ties are stronger than ever.

Castano is now dedicating himself more to political and propaganda work and is determined to get recognition for his group and gain it a place at the peace table, to ensure he is included in any amnesty a peace agreement would entail.