Abdul Ghani Baradar, one of Taliban's cofounders, has been named as the leader of its political office in Qatar amid talks with the United States to end the 17-year war.

Baradar is expected to join the talks, which appear to be gaining momentum, between Taliban representatives and US envoy to Afghanistan Zalmay Khalilzad in Doha to end what has been the US's longest-running military engagement so far.

Baradar, formerly a number two of the group, helped Mullah Omar - who died in 2013 - to found the Taliban movement in Afghanistan in 1994. He served in several key positions when the Taliban ruled Afghanistan from 1996 to 2001.

He fled to Pakistan after the US invasion in 2001 and was arrested in 2010 in an operation then considered to have dealt a fatal blow to the movement.

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Baradar was released from a prison in Pakistan in October last year after the first meeting in Doha - never confirmed by the US - between the Taliban and Khalilzad. He later joined his family in Afghanistan.

His release, according to security experts, was part of high-level negotiations led by Khalilzad with the Taliban.

David Sedney, deputy US assistant secretary of defense for Afghanistan and Pakistan under former President Barack Obama, called Baradar's appointment "a startling change ... that bodes very well for peace", adding that he was "more than cautiously optimistic" about the outcome of the talks in Doha.

"Ten years ago, Mullah Baradar led a dissident faction of the Taliban that wanted peace talks with the [Afghan] government of then President Hamid Karzai," Sedney told Al Jazeera.

"The government of Pakistan was opposed to those talks; they arrested Mullah Baradar and held him in prison until last fall during which time he was allegedly treated very roughly and perhaps even tortured."

Sedney said that following Baradar's release at the request of the US, "many people thought he would fade into the distance, but instead he has taken advantage of a fractured Taliban leadership and the desire of many Taliban for peace to reassert his authority".

"So this is a major, major change for the Taliban, and one that bodes very well for peace. Mullah Baradar has been on the side of peace for over a decade and this is a sign that there is great hope," Sedney added.

"Many things could go wrong, but there has been no such hope for peace in Afghanistan for almost the last 20 years."