Abdullah Ocalan, the charismatic Kurdish separatist leader once dubbed the "nemesis" of the Turkish state, is now seen as the best bet to end decades of armed insurgency.
The burly 64-year-old -- known as "Apo" or uncle to Kurds but branded a "baby killer" by Turks -- called on Thursday for a ceasefire in a letter penned from his isolated island prison cell to mark the Kurdish New Year.
Despite being behind bars since 1999, observers say Ocalan continues to pull the strings at the Kurdistan Workers' Party (PKK), the Marxist-oriented movement he founded in 1978 with a group of fellow students to fight for Kurdish autonomy.
His call for militants to lay down their arms and withdraw from Turkish soil came after months of clandestine talks with Turkey's intelligence agency aimed at ending the PKK's 29-year armed rebellion.
The man with a fiery gaze and bushy moustache born into a peasant family in Turkey's southeast has long been regarded by Ankara as a "terrorist leader" with blood on his hands.
He has spent half his life in exile, underground or in captivity.
"Nobody can solve this, but I can," his brother Mehmet Ocalan relayed him as saying after a visit to the remote Imrali prison compound off Istanbul in August.
In the prison, where for years he was the sole inmate, Ocalan spends much of his time reading books and listening to a radio tuned in to Turkey's state-run TRT station.
For five hours a week, he is also allowed to mingle and play sports with the compound's five other inmates.
Except for a few selected visitors, Ocalan has been mostly cut off from the outside world since his incarceration, but visiting Kurdish lawmakers say he is still "on top of things".
"Kurds have many political voices," Gulten Kisanak, a prominent Kurdish lawmaker, told reporters. "Mr Ocalan's duty is to coordinate between them and he is in the position to speak for everybody."
Addressed as "Serok" or leader within the ranks of the PKK, Ocalan was labelled the state's "nemesis" after leading his movement onto a path of armed struggle in 1984, with a plan to carve out a chunk of Turkey to found an independent Kurdish state.
By the time the PKK scaled down its bloody fight and gave up on its independence dream in return for greater autonomy, Ocalan had become Turkey's number one enemy, blamed for the deaths of some 45,000 people, mostly Kurds.
His first call for a unilateral ceasefire came in 1993, then again in 1995 and 1998, each time in return for a political agreement with Ankara, which refused to sit at the table with the "terrorist chief".
As violence escalated with every failed ceasefire attempt, Ankara acknowledged that its long-time foe might also be the best possible mediator to end the conflict.
Ocalan himself has apparently staked his future with the PKK on the March 21 ceasefire call.
"Consider Apo dead if this process fails. I am simply out," Ocalan was quoted as saying in a prison meeting with Kurdish lawmakers last month.
Mainly Turkish-speaking Ocalan became a left-wing militant during his university years in Ankara, where he studied politics.
In the early years of his exile he was given refuge in Syria, from where he led the PKK's armed struggle, causing major friction between Damascus and Ankara. Political pressure forced him out in 1998.
In February 1999, Turkish authorities nabbed him in Nairobi and swiftly sentenced him to death for treason. The sentence was commuted to life imprisonment when Turkey abolished the death penalty in 2002.
Imrali is notorious as the prison in the film "Midnight Express" which told the true story of a US student who escaped after being caught trying to smuggle hash out of Turkey.
Following Ocalan's arrest, the PKK -- which is classified as a terrorist group by both the European Union and the United States -- said it would strive only for cultural rights, entering its longest truce period which lasted until June 2004.
At the same time, Turkey undertook some timid reforms, allowing private schooling and radio and television broadcasts in Kurdish.
Despite his imprisonment, Ocalan is believed to retain strong influence over the PKK, raising hopes for a permanent peace.
"I want to solve the issue of guns with haste and without a single life being lost," Ocalan said in a recent letter from prison before Thursday's announcement.