Who is Abdullah Ocalan, the Kurdish militant leader urging peace with Turkey?

The 75-year-old militant leader Abdullah Ocalan has spent a quarter of a century in jail after leading his Kurdistan Workers Party (PKK) to take up arms against the Turkish state to fight for a Kurdish homeland. Now he is calling for peace. 

On Thursday, Ocalan, from his cell in Imrali island prison in the Sea of Marmara, south of Istanbul, called on the PKK to lay down its arms and dissolve itself, a move which if heeded by his fighters will bring an end to their 40-year insurgency and have wide-ranging implications for the wider region.

Ocalan, revered by the pro-Kurdish political movement but reviled by most Turks for starting the conflict in 1984, made the call four months after being urged to do so by an ally of President Tayyip Erdogan.

Both Erdogan and the opposition pro-Kurdish DEM party have voiced support for efforts to end the fighting that has killed more than 40,000 people, reshaped Turkish politics and scarred towns and cities across the southeast.

"I am making a call for the laying down of arms, and I take on the historical responsibility for this call," Ocalan said in a letter made public on Thursday by DEM party members after they had visited him in his prison cell.

Ocalan was captured in Kenya by Turkish special forces in 1999. Despite being jailed, he continued to wield considerable clout, but it is unclear how much influence he now retains over the PKK, whose fighters are mainly based in the mountains of neighbouring northern Iraq.

In his message on Thursday Ocalan urged his party to hold a congress and to formally agree to dissolve itself.

The idea of re-engaging with Ocalan was floated in October by an unlikely politician - Devlet Bahceli, an ultra-nationalist party leader and Erdogan's main parliamentary ally, who shocked the country when he suggested Ocalan could be freed if he succeeded in getting the PKK to end its insurgency.

STRUGGLE 'FILLED WITH PAIN'

Ocalan saw his profile peak during a 2013-2015 peace process between the Turkish state and his PKK fighters. Then prime minister, Erdogan regarded Ocalan as key to efforts to end the fighting. 

From his jail cell, Ocalan - affectionately referred to as Apo by Kurdish nationalists - rose in prominence. Photos in Turkish media showed a benign image of a grey-haired, moustachioed and smiling figure, in sharp contrast to past pictures of him in combat fatigues wielding an assault rifle.

"This struggle of our 40-year-old movement, which has been filled with pain, has not gone to waste but at the same time has become unsustainable," Ocalan said in a statement read to huge crowds at Kurdish new year celebrations in March 2015.

Those talks were the closest he was to get to achieving a negotiated solution to the conflict. Four months later the peace process collapsed and the conflict entered its bloodiest phase, focused in urban southeastern areas.

Today, the conflict is mainly centred in northern Iraq where the PKK is based.

Ocalan was born to a peasant family in the southeastern village of Omerli and his political ideas were shaped amid the violent street battles between left- and right-wing gangs in the 1970s.

He split from the Turkish left to found the PKK in 1978, pledging to fight for an independent state of Kurdistan after dropping out of Ankara University's political science faculty.

The PKK, designated a terrorist group by Turkey, the United States and European Union, was led by Ocalan from Syria until Turkey threatened war in 1998, forcing Damascus to expel him.

He sought refuge in Russia, then Italy and Greece before he was captured in the Kenyan capital Nairobi in 1999.

Appearing bewildered and dejected, he was flown to Ankara guarded by Turkish commandos, and sentenced to death. His sentence was commuted to life in jail, where he has remained ever since.