Karl Hopf (Ham, Westphalia, February 19, 1832 - Wiesbaden, August 23, 1873) was historian and expert in Medieval Greece, both Byzantine and Frankish.
Hopf has graduated on University of Bonn, where he got his Ph.D. in the medieval history of Greece. He was professor and librarian on University of Greifswald and University of Königsberg. He frequently visited Italian and Greek medieval archives finding sources for his works.