Karl-Heinz Gerstner

However, his legal father was actually his step-father, Paul Gerstner (1880-1945), an academic who taught Economics and hoped that his adopted son would grow up to become a statutory auditor.

His natural father was the diplomat Karl Ritter (1883-1968) who later became an ambassador.

Karl-Heinz Gerstner (15 November 1912 – 14 December 2005) trained as a lawyer and then worked during the war for the German diplomatic service in Paris.

Following the war he was released from internment as a Soviet prisoner of war after producing a number of affidavits testifying to his helpfulness to members of the French Resistance during the course of his time at the German embassy in occupied Paris.

He was then able to reinvent himself as an East German journalist.

Controversy later emerged, and has persisted, as to the nature and extent of his parallel career as a Stasi informer.

Karl-Heinz Gerstner was born in the Charlottenburg quarter of Berlin.

He attended the Kaiser-Friedrich Gymnasium (secondary school) in Berlin between 1917 and 1931.

In 1921 he became a member of the Youth Association and Path finder scouting organisations, remaining a member of the latter till 1930.

At school, he later recalled, a love of the French language and culture was awakened in him.

It was also during this period that he won a public speaking competition staged for Berlin school children by the Library of Congress in Washington.

His prize was six months abroad during 1928, as a pupil at the Tabor Academy, a prestigious private school in Massachusetts.

Renewed economic austerity following the Wall Street Crash triggered a period of accelerating political polarisation in Germany, and Gerstner chose the extreme left, in 1931 joining the "German Youth of 1 November 1929" scouting group, which tended to take its lead from the Communist Party.

Between 1931 and 1935 Gerstner studied Jurisprudence at Berlin's Frederick-William University (as the Humboldt was then known).

As a student he funded his living costs by working part-time at the foreign-exchange desk of the Deutsche Bank.

In 1931 he joined the socialist "Red students group".

He remained a member till 1932.

Fellow members whom he came across at this time included Friedrich Wolf, Harro Schulze-Boysen, Heinrich, Count von Einsiedel and the group's founder, Eberhard Koebel.

Towards the end of 1932 he began to take part in evening tutorials held by Kurt Georg Kiesinger.

On 1 May 1933 he joined the Nazi party: he was member number 2,673,178.

Party membership had surged since January 1933 when the Nazis took power and lost no time in transforming Germany into a one-party dictatorship.

That was followed by a six month period working at a solicitors' office in Berlin that specialised in cases that involved economics, where (despite the growing prevalence of state mandated antisemitism since 1933) two of the senior lawyers were of Jewish provenance.

Gerstner passed his Level 1 national law exams in 1935 and embarked on the next stage of the legal traineeship ("Rechtsreferendariat"), starting with six months at the district court in Rheinsberg.

For the next three years, between 1936 and 1939, he worked in Paris and the German foreign trade mission.

This appears to have counted, at least initially, as part of his "Rechtsreferendariat" (legal traineeship).

Gerstner was marked out for advancement soon after his arrival at Paris trade mission, partly on account of his excellent mastery of the language: the fact that during this time his father became the German ambassador to Brazil may also have counted in Gerstner's favour with German diplomatic staff in Paris.

After a few weeks he was offered a permanent position at the newly expanded trade mission, and his status as an "articled law clerk" was apparently suspended or overlooked.

He received his doctorate of laws from the University of Erlangen in 1937.

In August 1939 all the trade mission staff in Paris were returned to Berlin where Gerstner pursued his legal traineeship, employed as a "Gerichtsassessor" (loosely: "trainee judge").

Gerstner stayed in Germany for around six months.

During this time he met Sibylle Boden at a ski resort in the Riesengebirge (literally "Giant Mountains") in southern Silesia.

Boden, who later became a highly successful fashion designer, noticed the excellent quality of the suit he was wearing.

The simultaneous Invasion of Poland by Nazi Germany and the Soviet Union, launched in September 1939, had triggered the Second World War, and shortly after passing his law exams he received call-up papers requiring him to join the army.

However, in the end Gerstner was spared from military service as a result of injuries caused by childhood polio.

In February 1940 Gerstner finally completed his legal training, apparently passing the necessary exams.

Evidently there were other mutual attractions, since the two of them would quickly become a couple: in 1945 they married.

Nevertheless, in his autobiography published in 1999 Gerstner evidently identified an inconsistency which could not go unremarked.

He had taken the step, he wrote, only "out of hatred against Hitler ... in order [to do] something against the Nazis" (nur aus "Hass gegen Hitler ...um etwas gegen die Nazis" zu tun).

With half an eye on Gerstner's subsequent career as a German diplomat, there were commentators who found the explanation less than persuasive.

It was on the recommendation of the head of the legal department at Deutsche Bank that Gerstner wrote his doctoral dissertation on aspects of the modalities of interbank payments ("Treugiroverkehr").