Genghis Khan was a 13th-century warrior in central Asia who founded the Mongol Empire, one of the largest empires in history. By the time he died, the empire controlled a vast amount of territory in China and central Asia, and its armies had ventured as far west as Kiev in modern-day Ukraine. The successors of Genghis Khan would go on to control kingdoms with territories in the Middle East, South and Southeast Asia and Eastern Europe.
Despite his great achievements and ferocious reputation, there is much about Genghis Khan that we don’t know. For instance, there is not a single authentic portrait of the man that has survived to the present day. All of the images of him that exist were created after his death or by people who had otherwise never met him.
Additionally, until Genghis Khan gained control over the Uyghur people, the Mongolians did not have a writing system. As such, many of the records that survive of him were written by foreigners. An important Mongolian record that survives is called the “Secret History of the Mongols,” but was written anonymously (as its name suggests) apparently sometime after Genghis Khan’s death.
Source: livescience.com