Why was Genghis Khan portrayed as ruthless, and bloodthirsty?

The truth is most people portrayed him as bloodthirsty because he was so ruthless, but he wasn't really thirsting for blood. He was like all other conquerors who wanted power, territory, and wealth, he just used bloodthirsty and ruthless tactics. So he wasn't actually bloodthirsty it just seemed like it, but don't get me wrong he was ruthless, and used some pretty horrible tactics.