“The 43-year-old doused himself with a liquid and then set himself on fire” outside the courthouse in the western city of Krefeld on Wednesday, police said in a statement.
Bystanders doused the flames with blankets and a fire extinguisher, and a rescue helicopter took the man to hospital.
“According to witnesses, he said he was protesting against the detention of Ocalan and against German police violence,” said the statement, adding that they were also investigating a possible “personal motive” and mental health
Police said the man suffered “considerable injuries”. No one else was injured during the incident.
Last Friday was the 20th anniversary of the day when Turkish secret service agents caught Ocalan in Kenya, outside the Greek embassy in Nairobi — on February 15th, 1999.
Ocalan co-founded the Kurdistan Workers' Party (PKK) in 1978, an organization that is now blacklisted as a terror group by Ankara and its Western allies.
The PKK, originally set up to win Kurdish autonomy, became an armed group in 1984 with the aim of creating an independent Kurdish state. In the subsequent insurgency, more than 40,000 people have been killed.