German author, mathematician & writer, born in Estonia
Carl Gustav Axel Harnack (7 May 1851 - 3 April 1888) was a German mathematician known for his work in the field. Born in Tartu, he held German citizenship and completed his education at the University of Erlangen-Nuremberg. Harnack's doctoral advisor was Felix Klein, a renowned mathematician and educator. Sadly, Harnack passed away at the age of 36 in Dresden.