This is thought to be the only image of Mullah Omar (L)
It was Mullah Omar's backing for Osama Bin Laden which led to the US-led campaign to oust the Taleban.
Mullah Omar and Bin Laden go back to their time as resistance fighters against the Soviet occupation of Afghanistan of 1979 to 1989.
Mullah Omar vigorously defended his friend against allegations that he masterminded the devastating attacks on the World Trade Center and the Pentagon, accusing the US of trying to cover up their own intelligence failures.
Bin Laden is believed to have at least partially financed the Taleban takeover of Afghanistan, from which Mullah Omar emerged as "commander of the faithful", a title with great resonance in Islamic history.
The ties may go further. It was thought that Mullah Omar has taken Bin Laden's eldest daughter as a wife, and that Bin Laden may even have taken one of Mullah Omar's daughters as a fourth wife.
The Taleban always denied this.
Hermit
No Western journalist has ever met Mullah Omar, who left virtually all contact with the outside world to his foreign minister, Wakil Ahmad Mutawakkil.
To many ordinary Afghans he is just a name, but those who have seen him say he is relatively young - in his early 40s - and tall, with a black beard and a black turban.
His right eye was damaged by shrapnel when he was fighting Afghanistan's Soviet occupiers in the 1980s.
When the Taleban were in power he rarely left the southern city of Kandahar where he lived in a large house that was reportedly built for him by Bin Laden.
The two were reported to have spoken daily by satellite telephone, and some reports suggested they also met for fishing trips.
Invisible fist
Under Mullah Omar's rule, a strict interpretation of Islamic law was imposed on Afghanistan under Taleban control.
Women were strongly discouraged from leaving their homes, denied schooling and jobs and forced to fully cover themselves.
Women found guilty of adultery were stoned to death, homosexuals crushed under brick walls, thieves' hands amputated and murderers publicly executed by victims' families.
Edicts from Mullah Omar included the death sentence for anyone converting to another religion, as well as the infamous orders to destroy the country's ancient Buddha statues at Bamiyan.
The Taleban's fall from power was a far cry from the optimism that greeted their arrival in Kabul in the mid-1990s, when many ordinary Afghans welcomed them as heralding an end to the chaos caused by years of civil war.
Now they are likely to be remembered for the protection they gave a foreigner, Bin Laden, than for anything they did for Afghanistan.