In Dan Carlin's Hardcore History podcast, he says that we only have two historical sources of information pointing to Genghis Khan's appearance:
He, at some point, was disappointed that his firstborn did not have his red hair.
Someone described him as having "tiger eyes", what some people interpret as a sign that he had green eyes.
Both these characteristics are very far from how he is usually depicted in the media. Do we really only have these two historical sources? What do current historians believe?
Here's a previous thread discussing the subject, if you're interested:
https://www.reddit.com/r/AskHistorians/comments/2pxkrr/what_did_genghis_khan_look_like/
Edit: /u/quickspore made a great post in there, since I have been asked to link to specific users who answered the question then.