Harnack, Arvid, born 24-05-1901, in Darmstadt, 
Germany and his family were prominent and academically gifted Protestant Germans from the Baltic region. His father was literary history professor Otto Harnack 
and his mother was Clara Harnack (born Reichau),an artist. Reichau was the granddaughter of Justus von Liebig, 
one of the principal founders of organic chemistry. Harnack’s siblings were Falk Erich Walter Harnack, 
his elder brother; Inge Harnack; and Angela Harnack, a violin teacher. Harnack was the nephew of theologian Adolf von Harnack, 
Falk Harnack (2 March 1913 – 3 September 1991) was a German director and screenwriter. During Germany’s Nazi era, he was also active with the German Resistance and toward the end of World War II, the partisans in Greece.
In 1919 Arvid became a member of the Freikorps, 
a volunteer militia. From 1919 to 1923 he studied law at the Friedrich Schiller University, the University of Graz, and the University of Hamburg; he became a Doctor of Law in 1924. He completed postgraduate studies in economics in Hamburg and the London School of Economics before being awarded a Rockefeller scholarship to study at the University of Wisconsin. In Madison, Wisconsin, Harnack was influenced by the industrial economist and labor historian John R. Commons, 
and saw him as a mentor.
In 1926, Harnack met American literary historian Mildred Fish, 
also a graduate student at the Wisconsin University, after Harnack wandered into the wrong lecture hall. Mildred “Mili” Elizabeth Fish-Harnack (born Fish; 16-09-1902, in Milwaukee, Wisconsin, United States
After a brief friendship and romance, they were engaged on 06–06-1926 and married on 07-08-1926. The couple met Margaretha “Greta” Lorke, 
a German student of sociology, at a Friday evening gathering organized by Commons in Madison. A friendship that lasted for many years developed between Mildred and Lorke, the latter being drawn into an intimate group of Wisconsin radicals known as the Friday Niters Club. According to a fellow student and member of the group, Hazel Briggs Rice, the Friday Niters Club members considered themselves to be liberal Progressives. Lorke later married Adam Kuckhoff. The Harnacks’ Friday Niters Club was a preface to their involvement in what became known as the Sacco and Vanzetti case, which became a cause célèbre. Many in the group protested the planned execution of the pair, and Arvid petitioned the governor to create a committee to investigate the controversy. The trial radicalised the Harnacks.
At the end of the semester in March 1928, Arvid returned to Germany, as his fellowship had ended, while Mildred stayed for another year to complete her studies before moving to Germany on 02-06-1929, at which point the couple lived in the small university towns of Jena and Giessen.
On 08-08-1935, three months after Harnack joined the trade ministry, he met with Hirschfeld in a meeting that lasted three hours. During the meeting, Hirschfeld informed Harnack that his position in the trade ministry could provide useful information that could be used to defeat the Nazis, and offered to establish a system to convey the documents to Moscow. Harnack agreed to be an informer and was given the codename Balt, assigned a control officer, Alexander Belkin, and given a mission to increase his sources by building a network of contacts. However, Hirschfeld requested that Harnack break off all relations with the KPD, and to avoid working for the resistance, but Harnack refused; he was never interested in becoming a Soviet agent, considered himself a communist, and would supply information to anybody who would take part in anti-fascist operations that helped to destroy the Nazis. According to KGB sources, between 1935 and 1938 Harnack supplied information about German currency, German investments abroad, and details of the German foreign debt. He also provided details of secret trade agreements to Soviet intelligence. During that period, Harnack circulated the same information to other groups.
In 1935, Harnack met Harro Schulze-Boysen 
for the first time, but Harnack decided not to meet again due to their different temperaments Harro Schulze-Boyse was a left-wing German publicist and Luftwaffe officer during World War II.
In 1940, Harnack came into contact with other resistance groups and began to cooperate with them. The most important of these was a small group called Gegner Kreis that was run by Harro Schulze-Boysen, a Luftwaffe leutnant and descendant of an old German military family, who had known Harnack since 1935, but was reintroduced to him sometime in late 1939 or early 1940 through Greta Kuckhoff. The Kuckhoffs had known the Schulz-Boysens since 1938, and started to engage them socially in late 1939 or early 1940 by bringing Mildred and Libertas “Libs” (Harro’s wife) 
together while on holiday in Saxony. Harro Schulze-Boysen was hanged on 22-12-1942 (aged 33) in the Plötzensee Prison.Libertas “Libs” Schulze-Boysen was also hanged 22-12-1942 (aged 29) in the Plötzensee Prison.
In June 1941, after the German invasion of the Soviet Union, the resistance group intensified its leaflet propaganda.[83] At the same time, the group started to collect military intelligence in a careful, systematic manner that could be used to overthrow the Nazis.[83] Members of both groups were convinced that only Germany could only be liberated by the Nazis’ military defeat, and that by shortening the war, millions of people could be saved.
On 07-09-1942, the Harnacks were arrested by the Gestapo while on a short holiday to Preila on the Curonian Spit.
Death and burial ground of Harnack, Arvid and Mildred “Mili” Elizabeth Fish-Harnack.
Arvid was sentenced to death on 19-12-1942 after a four-day trial before the Reichskriegsgericht (“Reich Military Tribunal”), by jurist Roland Freisler 
and was put to death three days later at Plötzensee Prison in Berlin. 
He and his co-conspirators were hanged from meat hooks by piano wire, a method designed to prolong their suffering. Mildred was originally sentenced to six years in prison, but Hitler swiftly cancelled the sentence and ordered a new trial, which resulted in a death sentence. Mildred 
aged 40, was beheaded by guillotine on 16-02-1945 and her body was released to Hermann Philipp Rudolf Stieve, 
anatomy professor at Humboldt University, to be dissected for research. Much of Stieve’s research was conducted during the 1930s, after the Nazi Party had come to power in Germany. He did not join the party himself, but as an ardent German nationalist supported Adolf Hitler in the hope of restoring national pride. The Nazis imprisoned and executed many of their political opponents, and their corpses became Stieve’s primary research material, with his full awareness of their origin. While much of his work is still considered valuable—among other things, he provided scientific evidence that the rhythm method was not effective in preventing pregnancy—it is considered tainted by his effective collaboration with the Nazi regime’s political repression, especially in light of its later genocides. Herman Stieve died 05-09-1952, aged 66, in Berlin.
A cenotaph was installed for the Harnacks after the war by Arvid’s older brother Falk, a member of the White Rose resistance group, at Zehlendorf Cemetery. Mildred is buried there and the ashes of Avrid are buried at the Plötzensee cemetery in a anonymous grave between many other victims.
