Prior to the story Geoffrey was a geneticist in the army. He is known to have worked alongside Bernard Senior for a long-time.
Following Bernard Senior's latest failure to transfer Samuel's brain to a shell, Geoffrey proposed that he used a living shell instead (this being a human whose mind has been erased by a pathogen), though Bernard Senior was horrified at this.
Some point later he met and became friends with Greybane. Learning of Greybane's abilities he aimed to utilise them for the best of mankind, though the outbreak of the zombie virus halted his plans.
In an attempt to combat the zombies Geoffrey tried to modify the genes of two soldiers (Greybane and Bug) to become strong enough to counter the zombie outbreak. Geoffrey's operation went awry however, and Bug was horribly mutated.
Upon discovering his new state Bug went berserk, critically injuring Geoffrey in the process. After Greybane awakes Geoffrey beseeches him to keep him alive. Complying, Greybane injected Geoffrey with the zombie virus, before locking him in the basement of a house near New Hammerston where he remains.
Some time later he was discovered by Nina, who labelled him Zomgack.
Geoffrey is shown in a flashback working on the Immortal Brain Project alongside Bernard Senior.
Being a zombie Geoffrey has no discernible personality.
Prior to his transformation he appears to have been quite a utilitarian character, seeing nothing wrong in generally unethical practice if the end product would make up for it.
Due to his zombie state Geoffrey has no real relationships.
Although he no longer recognises him, Geoffrey and Greybane were once close friends (to the extent that Greybane felt the need to hunt Bug for his wounding of Geoffrey.
Geoffrey worked alongside Bernard Senior for some time. Despite this the two don't appear to have been close, Bernard Senior referring to him as "Dr. Rawlings" despite his insistence that he call him Geoffrey.
Geoffrey is like most zombies: mindless, weak and without even the ability to talk.
When human he appears to have have a great mind.