DOOM | Cyberdemon Boss

The cyberdemon was the most significant and prized creation of the UAC's Lazarus Project, brought back to life and enhanced with technology in an effort known as the Cyberdemon Reanimation Project. A manned expedition to the Titan's Realm, discovered the petrified remains of a Baalgar demon, an ancient shadow lord previously known only from mention of a battle in which it fell in the Corrax tablets, found in the UAC automated survey of 2143.
The project to revive the Baalgar demon began as attempts to merely weld the creature's body back together for educational and "inspirational" display purposes, but it was found that application of Argent plasma to the petrified remains reanimated the long-dead tissue. After this, the Lazarus researchers became obsessed with reviving and enhancing the demon for use as a bioweapon, integrating an Argent accumulator into its chest with direct control from the brain as a near unlimited, on-demand power supply, and grafting a powerful arm cannon in place of the missing left arm.
Once the cyberdemon was complete and the Argent accumulator activated, however, the demon immediately turned the device to full power, reviving neural and circulatory functions, and began attacking the researchers. One Follower Jacobson sacrificed himself by luring the cyberdemon into Holding Pen 6, where it was permanently detained. Due to an inability to subdue the demon again, it was put into a permanent state of suspended animation, and only reawoke when Olivia Pierce unleashed the Hell wave from the Lazarus Labs.