In 1984, he launched his Kurdistan Workers' Party (PKK) -- then six years old -- onto a path of armed struggle which has continued to this day, interspersed with periods of truce, and has cost an estimated 37,000 lives.

In February 1999, the Turkish authorities finally laid hands on the man who had become their public enemy number one, capturing Ocalan in Nairobi, Kenya, with help from Israeli agents.

After having been brought to Turkey and imprisoned on an island in the Marmara Sea, he was put on trial and swiftly sentenced to death for separatism and treason.

His sentence was commuted to life imprisonment when Turkey, anxious to advance its candidacy to join the European Union, abolished the death penalty.

Ocalan, a burly 57-year-old from the southeastern province of Sanliurfa, is seen by non-Kurdish Turks as a dangerous terrorist, and by many Kurds as a hero.

The organisation he founded is classified as a terrorist group by both the EU and the United States, but Ocalan, after his arrest, has on several occasions expressed willingness to give up violence.

In the 22 years since it began its armed struggle, the PKK declared four truces, the longest lasting from Ocalan's arrest in 1999 until June 2004.

In 1999, the PKK said it renounced its quest for an independence state and would strive only for cultural rights.

At the same time, Turkey undertook some timid reforms, allowing private schooling and radio and television broadcasts in Kurdish, more under pressure from the EU, with which it began membership talks in October 2005, than the PKK.

In the early years of his exile, Ocalan was given refuge in Syria, causing major friction between Damascus and Ankara, which at one point threatened military action.

After the 2003 allied invasion of Iraq, Ankara's relations with Washington and Baghdad cooled when Turkey blamed the two for failing to take decisive action against PKK militants who use bases in the mountains of Kurdish-populated northern Iraq to infiltrate Turkey.

Despite his imprisonment, Ocalan is believed to retain strong influence over the PKK, which has been plagued by infighting since his arrest.