Genghis Khan was a historical figure in ancient Earth history.
In 2266, Korby believed that by transferring consciousness into an android body, a Human would have practical immortality. James T. Kirk responded that this was programming. He continued further by saying that others had made the same promises, using different words, and that these others were Genghis Khan, Julius Caesar, Adolf Hitler, Ferris, and Maltuvis. (TOS: "What Are Little Girls Made Of?")