Dr. Carmack discovered skeletal remains on Mars that contain a 24th chromosome (dubbed C24), making the creatures superhuman, invulnerable to disease and with the ability to rapidly heal injuries. Carmack experimented with C24 and deliberately injected the chromosome into a convicted prisoner Curtis Stahl, a multiple murderer. This became Carmack's own undoing as Stahl mutated and broke free and began to kill the scientists and causing an outbreak of mutated monsters. Carmack managed to transmit a warning before he was attacked by 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 laboratory. However, Carmack was revealed to be infected by C24 and mutated into an Imp and attacked Duke. However, Duke lured Carmack to become entrapped in a nanowall.
- His last named is a reference to Doom series creator John Carmack.