Genghis Khan was a Mongol Human dictator of Earth's 12th and 13th centuries, on a par with Julius Caesar, Adolf Hitler, Ferris, and Maltuvis.
James T. Kirk mentioned Genghis Khan to Roger Korby in 2266, after Korby implied human programming leading to near-practical immortality as the major impact of transferring the Human consciousness into an android body. (TOS: "What Are Little Girls Made Of?")
In 2269, an image of Genghis Khan was created by the Excalbians in a plot devised to better understand the concepts of "good" and "evil". (TOS: "The Savage Curtain")
Genghis Khan was played by actor Nathan Jung. His title means "Greatest of All Rulers."