Abdullah Ocalan inspires a fierce loyalty among Kurdish nationalists matched only by the hatred in which he is held in most of Turkey.
More than 29,000 people have died in the ruthless separatist campaign Mr Ocalan has directed in Turkey's south-east for 14 years. Ankara holds him personally responsible for all those deaths and his capture represents a massive victory for Turkey, where he is reviled by the popular press and across the mainstream political spectrum as a mass-murderer and a "baby killer".
Last seen in Italy in January, he has lived in shadowy exile since 1980, setting up a network of militant sympathisers in Western Europe. Late last year several set themselves on fire to protest at his detention in Italy, before a Rome court said he could go free.
Since then Mr Ocalan had been on the run, as European states rebuffed his applications for refuge.
Turkey vowed to chase him to the ends of the earth.
"Wherever he goes in the world, we will pursue him . . . Those who befriend him are the partners of a baby-killer," Turkish President Suleyman Demirel said.
Mr Ocalan, whose nom de guerre is "Apo", retains a Cold War brand of nationalism mixed with Marxist-Leninism. "You must believe before everything else that the revolution must come, that there is no other choice," he said in a televised address to Kurdish youth in August last year.
"Even though I am 50 years old I have never allowed myself to get old. I am going on with the struggle."
He was driven from Syria in October after Ankara threatened Damascus with force if it did not wind up bases it said the PKK was using to launch raids in Turkey's southeast.
From there he fled to Moscow, before appearing in Rome.
Mr Ocalan, born to a poor peasant family in the south-eastern village of Omerli, forged his political ideas in the violent atmosphere of Turkish politics in the 1970s.
About 5,000 people were killed in street fighting between left and right which ended when the army staged a coup in 1980.
Mr Ocalan, a dropout from Ankara University's political science faculty, fled abroad after the putsch. He founded the PKK in 1974 as an extreme-left nationalist faction which later earned a reputation for ruthlessness by killing members of rival groups, Kurdish landlords and pro-government tribesmen.
Fourteen years ago he launched his war against the Turkish state for the establishment of an independent state of Kurdistan along Marxist lines.
The PKK announced "liberated zones" and Turkish forces rarely travelled through the region at night for fear of ambush.
But a tough military scorched-earth campaign against the rebels and their civilian supporters has since pared back the group's numbers and badly weakened its ability to strike.
"War is war and this war is the dirtiest and cruellest in the world," Mr Ocalan told MED TV last month.
He gradually dropped demands for independence and said he could end the conflict if Turkey granted Kurdish autonomy or cultural and linguistic rights.