Ankara: When Turkish authorities arrested Kurdish militant leader Abdullah Ocalan two decades ago, it struck a blow to his outlawed separatist group but experts say his influence remains significant as a key player in any future peace deal.
Ocalan founded the Kurdistan Workers' Party (PKK) -- blacklisted as a terror group by Ankara, the United States and the European Union -- in 1978 with a group of fellow students to seek Kurdish autonomy.
The party became an armed group from 1984, with the objective of creating an independent Kurdish state. More than 40,000 people were killed during the PKK's insurgency.
Prior to his 1999 arrest, Ocalan was in exile in Syria until Damascus and Ankara reached an agreement in 1998 and he was forced to leave.
He was eventually caught in Kenya outside the Greek embassy in Nairobi on February 15, 1999 by Turkish secret service agents.
Now he is in a notorious prison on Imrali island off Istanbul and despite almost complete isolation remains a reference figure for the Kurdish cause not just in Turkey but across the region.
"Ocalan's arrest was initially a huge blow to the organisation, because he had controlled every aspect of the PKK and its activities and suddenly he was gone," said Aliza Marcus, author of the book "Blood and Belief: The PKK and the Kurdish Fight for Independence".
"In addition, his decision to suspend the war and basically give up on an independent Kurdistan -- as he announced at his trial -- added a whole new layer of confusion," she said.
But the PKK has been able to adapt, "partly because Ocalan was able to communicate from prison, through interviews and meetings with his lawyers", Marcus said.