Mullah Baradar, freed by Pakistan after more than three years in detention, was once the right hand man of the Afghan Taliban's supreme commander Mullah Omar.
Baradar was arrested in Karachi in early 2010 in a joint operation between the CIA and Pakistani intelligence.
His capture was hailed as evidence of the successful "war on terror" partnership between Washington and Islamabad which later descended into acrimony and bitterness.
But his release has been sought by Kabul as part of efforts to help the struggling Afghan peace process, though it is unclear what authority he commands after three years in Pakistani custody.
With Omar still on the run, Baradar was the most senior member of the Taliban held after US-led troops invaded Afghanistan in the wake of the 9/11 attacks, bringing down the Islamist regime.
His capture allowed the Pakistanis, often accused of playing a double game with the West by secretly supporting the Taliban, to show its good faith with Washington.
But it also allowed Pakistan to keep a close eye on a man who could play an important role in potential peace talks in Afghanistan.
Born in 1968 in the southern province of Uruzgan, Abdul Ghani Baradar fought the occupying Soviet forces in the late 1980s before becoming one of the founding members of the Taliban movement.
When the Taliban took power in Kabul in 1996 after years of chaotic civil war, the young Baradar was a trusted friend of Omar and rose to become the movement's top military strategist.
After the fall of the Taliban, senior militants fled across the border to rear bases in Pakistan, where Baradar became a member of the so-called Quetta Shura, the movement's ruling council.
The shura, led by Omar, is widely reported to have its headquarters in Quetta, the capital of Pakistan's insurgency-hit southwestern province of Baluchistan, though Pakistani officials deny this.
Baradar was seen as more open to a negotiated end to the Afghan war than Omar -- hence in part the desire for his release.
But analyst Rahimullah Yusufzai said Baradar's significance had been greatly eroded by his time in Pakistani custody and it was unlikely the Taliban would accept him as a mediator, fearing he had come under the sway of Pakistani intelligence.
A mid-ranking Taliban official agreed, saying he expected Baradar would live quietly in Karachi, perhaps ferrying messages from time to time but not regaining his role in the Quetta Shura.