Achim Gercke (August 3, 1902 – October 27, 1997) was a German politician. Born in Greifswald, Gercke became a department head of the NSDAP in Munich on January 1, 1932. In April 1933, he was appointed to the Ministry of the Interior, where he served as an expert on racial matters. In that year in a speech to a general audience, he stated that beside the task of maintaining one's own blood as pure, there was the task of "extinction", which would obey the great law of Nature to eliminate the bad and so be truly humane.
Gercke devised the system of "racial prophylaxis", forbidding the intermarriage between Jews and Aryans. As a student, he had attempted to develop a card index listing all Jews in Germany. His articles outlined Nazi public thinking on what to do about the Jews at the beginning of the Third Reich, which includes expelling them all from Germany. It notes that the just-issued Nuremberg Laws restricting Jews were provisional measures that indicated the direction future measures would take. He argued for a Jew being any person with one-sixteenth Jewish blood.
When Gauleiter Rudolf Jordan claimed that Reinhard Heydrich had Jewish ancestry and therefore could not have been Aryan, it was Gercke who investigated the issue and concluded that Heydrich was a pure Aryan with no Jewish ancestry. In 1935 he was dismissed following charges of homosexuality, possibly fabricated by rivals associated with his successor. After the war, he worked as an archivist and town clerk.