Harnack's a surname and may refer to: Adolf von Harnack (1851–1930), German liberal theologian and historian of religion Arvid Harnack (1901–1942), anti-Nazi resistance fighter Carl Gustav Axel Harnack (1851–1888), German mathematician Ernst von Harnack (1888–1945), anti-Nazi resistance fighter Mildred Harnack (1902–1943), anti-Nazi resistance fighter Theodosius Harnack (1817–1889), theologian Harnack's principle… (More on Harnack)