The toughest enemy in Doom. Was described by id as: "A missile-launching skyscraper with goat legs. 'Nuff said". The CyberDemon was the 'boss' at the end of Episode 2 (The Shores of Hell) of the original Doom, and also featured heavily in all subsequent Doom games.
A supremely cool (if slightly small at 3.5") pewter statue of the CyberDemon is availabe in the id Anthology collector's pack.