Mark Donald Steger (born January 16, 1962) is an American actor, performance artist, and choreographer. He portrays the Demogorgon in season one of Stranger Things.

Mark is also known for his work on I Am Legend (2007), Heroes: Going Postal (2008), American Horror Story (2013), Paranormal Activity: The Ghost Dimension (2015), and The Last Witch Hunter (2015).