Historically, khans were Central Asian emperors, nobles, and military leaders. One of the most famous was Genghis Khan, ruler of the 13th-century Mongol empire.
The power held by someone with the title of khan depended on the country or region. In some places a khan was the most powerful ruler, and in others the khan merely controlled an army or small nomadic tribe. While the use of khan as a title faded after the Middle Ages, it became a common surname among South and Central Asian Muslims. Khan's Turkic root is khaqan, or "ruler."