The latest trial concerning the book "Vermächtnis - die Kohl-Protokolle" ("Legacy - the Kohl Transcripts") opened in a Cologne court on Thursday.

Helmut Kohl, now 85, is suing principle author Heribert Schwan - formerly his official ghostwriter - for 5 million euros ($5.44 million) in damages. The case is also against co-author Tilman Jens and publishers Random House. Kohl argues that the defendants had no right to publish material from his conversations with Schwan without his consent.

Prior to the trial, Random House's lawyers had described the sum as "unrealistic," given that the highest such damages so far awarded in German courts totaled 625,000 euros, won by TV meteorologist Jörg Kachelmann.

Presiding judge Martin Koepsel gave no indication on Thursday as to the court's opinion of Kohl's 5 million-euro target.

Ghostwriter returns to haunt employer

Heribert Schwan has had a distinguished career with regional public broadcaster WDR

Schwan, an acclaimed broadcast and print journalist, once worked closely with Kohl - in the book, he describes how the former chancellor had taken to referring to him as "Dichter," meaning poet, writer or scribe. He even claims that Kohl at one point made reference to another book Schwan would one day write, perhaps after his death, concerning their time together.

Together, they compiled three volumes of the chancellor's memoirs - based on hundreds of hours of talks held between 2001 and 2002. Before the fourth and final volume was written, however, Kohl and Schwan fell out and broke contact. As Schwan describes it, having devoted a lengthy opening chapter of the 2014 book to his first legal battle with the chancellor, their working relationship broke down after Kohl remarried, and Maike Kohl-Richter took greater control of her new husband's affairs.

The timing of the interviews, in hindsight, may have been crucial to the tone of the warts-and-all unauthorized biography. Schwan and Kohl were working soon after Kohl's political career's end when the rambunctious Rhinelander felt betrayed and abandoned by former allies. During their time together, Kohl's first wife Hannelore committed suicide; Schwan devotes a passage to his surprise, days after her death when Kohl rang to ask why the ghostwriter had not turned up for their latest appointment.

Merkel the liability, USSR 'up the creek'

The original version, no longer available due to separate litigation which Kohl won, bristled with quotes showing the sharp-tongued Christian Democrat at his most frank and furious.

After stopping work with Schwan, Kohl published memoirs of his own

Describing the early political career of Angela Merkel, Kohl's former protégée, who turned against him during the expenses scandal that ended his political career, Kohl recalled how she "couldn't even hold a knife and fork properly," saying she "hung around at state dinners so that I had to tell her repeatedly to pull herself together."

As to his right hand at the CDU, Wolfgang Schäuble, long considered a likely successor as chancellor, Kohl makes it clear he didn't trust his conviction in the European Union - saying he decided to stay on as chancellor to lay the foundations of the single European currency.

On the issue of the fall of the Iron Curtain and German reunification, Kohl also offered a frank verdict on what moved Soviet leader Mikhail Gorbachev to dissolve the USSR, suggesting it had more to do with bankruptcy than political principles. "Gorbachev looked at the books and had to concede he was up the creek without a paddle," Kohl was quoted as saying.

In the case of US President Ronald Reagan, one of Kohl's more backhanded compliments was that the former film star, at least, acknowledged when he was out of his depth on international issues.

The original hardback copy has since been heavily redacted, removing many of the key block quotes from Kohl's conversations with Schwan. This follows Kohl's successful efforts to remove them, on the basis that Schwan was contractually bound to publish only with Kohl's consent. Schwan had argued that the conversations' content were in the public interest. A court forced Schwan to return the original tapes of the conversations to the Kohl estate, although he still possesses copies.

A verdict on Thursday's damages lawsuit is expected on June 2. The verdict should also include a decision on whether Schwan can retain copies of his conversations with the former chancellor.

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