Charles Gilbert Chaddock was born in 1861 in Jonesville, Michigan. He qualified in medicine in 1885, and worked at the North Michigan Asylum in Traverse City. He spent a year studying in Europe in 1888. He became Professor of neurology and psychiatry at the Marion-Sims College of St. Louis University. He returned to Europe in 1897, spending most of the time as assistant to Joseph Babinski. On his return to the United States in 1899 he introduced American physicians to Babinski's sign, later publishing a translation of Babinski's work.
Chaddock introduced his eponymous reflex in 1911, calling it the External Malleolar sign. He also described an analogous sign in the upper limb. He is also credited with the first use of the word homosexual in the English language, as well as the first use of the word bisexual in its current sense of being sexually attracted to both women and men, in his translation of Richard von Krafft-Ebing'sPsychopathia Sexualis in 1892. Prior to this, "bisexual" was usually used to mean hermaphroditic.