Karl Haberstock's first career was in business, as a bookkeeper in his native Augsburg and later Brussels. He returned to Germany on the death of his father in 1900, and worked for three years in banking before setting up his first store, selling porcelain, in Würzburg. He began to sell pictures, and shortly there after moved to Berlin. By 1912 he was successful enough to move his shop to he Bellevuestrasse, selling mostly German 19th century pictures and some old masters. His success continued and by the 1920s he was selling higher priced pictures to an international clientele.
Haberstock was thus well established in the art trade when the Nazis came to power in 1933. He joined the Nazi party that same year and insinuated himself into the Nazi elite. In 1936 he sold his first picture to Hitler, a Paris Bordone Venus and Amor which he had acquired in 1928, and began to sell to other Nazi leaders such as Goering and Goebbels. His most important customer remained Hitler, to whom he sold over 100 works between 1936-1938. In that year he moved his gallery to an even better space on the Kurfürstrasse in Berlin, where he remained until it was bombed in 1944.
One of Haberstock's most important connections to the Nazi leadership was Hans Posse, whom he had recommended as the first director of Hitler's planned museum in Linz. Haberstock also participated in the disposal of the "degenerate" art which had been removed from German state museums. Haberstock's influence within Nazi circles diminished substantially upon Posse's death in 1942, when he lost his access to Hitler and the Linz project.
Haberstock made regular trips to Paris throughout the occupation. While there he dealt with French agents and dealers who acquired paintings for him. He did not deal directly with ERR (Einsatzstab Reichsleiter Rosenberg) in Paris but may have had ERR loot pass through his hands. He is not known to have personally visited the Jeu de Paume repository for looted art.
Haberstock was arrested in May 1945 by the Allies and was interrogated and later moved to a Civilian Internment Camp where he remained until 1946. Haberstock later moved to Munich and resumed his art dealing business. He died in 1956. [biography summarized from Jonathan Petropoulos, The Faustian Bargain, 2000, p. 74-98]
Rousseau, Theodore, Jr. Detailed Interrogation Report No. 13. Subject : Karl Haberstock. 1 May 1946 [National Archives and Record Administration; copy National Gallery of Art Archives, S. Lane Faison papers, box 2]
Petropoulos, Jonathan. The Faustian Bargain: The Art World in Nazi Germany. New York, 2000:74-100