After the UAC discovered the fossilized remains of Mars' original inhabitants, Dr. Carmack studied the remains and subsequently harvesting their genetic remains, which contained a 24th chromosome (dubbed C24). Carmack and his colleagues studied C24 and learning that it granted the Martians superhuman abilities, making them invulnerable to diseases and with the ability to rapidly heal injuries.
Carmack began experimenting C24 and using human convicts as live test subjects, who are injected with C24. This became Carmack's own undoing as one of the prisoners, Curtis Stahl, mutated and broke free, and began to kill Carmack's colleagues and causing an outbreak in the facility. Carmack managed to transmit a warning to Earth before he was attacked by the mutated Stahl.
Carmack was later found alive by the Rapid Response Tactical Squad. The doctor was deranged to the point of tearing off his own ear before he was restrained and taken to Dr. Samantha Grimm's lab. However, Carmack was revealed to be infected by C24 and mutated into an Imp, and attacked Duke and Samantha. Duke managed to trap Carmack in the lab's nanowall. The mutated Carmack was eventually executed by Sarge.
- Dr. Carmack is named after Doom series creator John Carmack.