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Unknown to most of the characters in the game, the Hecatomb is actually the real Curtis Craig: having started out as a relatively ordinary human child, Curtis enjoyed a happy and untroubled life with his family - right up until his father Jonas decided to take him along to work at Wyntech. At the time, Wyntech CEO Paul Warner was experimenting on the dimensional rift known as the Threshold and needed Jonas' assistance in ensuring that human test subjects were available for testing the portal. It was during one of these experiments that their current subject died before he could be sent through, forcing Jonas to leave for more test subjects - and leaving Curtis alone in the laboratory with Warner.
With the Threshold in danger of closing, Warner grabbed Curtis and threw him into the rift: arriving in Dimension X otherwise unharmed, Curtis was studied at length by the Threshold-Dwellers and quickly became the basis of their first experiment on Earth. Taking a sample of their new test subject's brain tissue, they used it to sculpt a perfect replica of Curtis from dead rats and protoplasmic slime, before sending the newly-formed clone back through the portal to Earth. Suspecting the truth but unwilling to actually believe it, Jonas accepted Warner's lie that there'd merely been an accident, and allowed the duplicate to take Curtis' place; meanwhile, Warner began a partnership with the Threshold-Dwellers, keeping "The Twin" under close observation on their behalf.
However, the real Curtis Craig was still alive beyond the Threshold. Horribly disfigured by exposure to the alien atmosphere of Dimension X, he only survived thanks to the intervention of the Threshold-Dwellers, who created an organic life-support system fueled by cannibalized organs - a plentiful resource thanks to their partnership with Warner. As his mutations continued, Curtis also began developing psychic powers, allowing him to telepathic peer across the Threshold and observe the family that had been stolen from him.
Driven half-insane by loneliness and anger, Curtis began plotting revenge against his doppelganger: realizing that he could seize control of the clone's body if his mind were to lose its grip on reality, he gradually conceived of a plan to drive the replica insane. To that end, he began slowly exercising his new powers, building his strength until he was capable of destroying a human mind.
A Year Ago
Twenty sleepless years after he was first imprisoned in Dimension X, Curtis made his first attempt to break his clone's mind: however, his psychic assault also caused the clone to start remembering the events of his creation and arrival on Earth - and for a brief time, he was aware of who and what he really was. Furthermore, Warner was still keeping the clone under observation, and upon discovering that his prize test subject appeared to be suffering a meltdown, he quickly had the duplicate committed to a mental hospital for closer observation.
Here, the clone was subjected to vicious treatments and punishments at the hands of the sadistic Dr Marek. Ironically, Marek's brutal courses of electroshock therapy were able to disrupt Curtis's attempts at seizing control of the replica's mind; frustrated by the failure of this first attempt, Curtis returned to plotting, vowing to try again later.
While the clone slowly recovered, the real Curtis gradually developed the ability to manifest himself on Earth as a mental projection - which he called the Hecatomb, soon to become his alias throughout the main game. Eventually, the clone (now known only as Curtis for the sake of brevity) left the mental hospital and rejoined the workforce at Wyntech - and the Hecatomb's newest plot for revenge began.
A Puzzle Of Flesh
Once again, the Hecatomb begins tormenting Curtis with visions, hallucinations and nightmares in an attempt to break his mind. This time, his ability to project physical force this time allows him to also murder his friends and coworkers, ensuring that Curtis ends up as the prime suspect in the ensuing police investigation; with stress levels climbing and belief in his own sanity plummeting, Curtis at times even suspects himself as the game continues.
The Hecatomb first targets Bob, a disagreeable coworker with whom Curtis had been arguing with earlier that day, perforating him with knives; moving on to Tom, one of Curtis's more reasonable superiors, he beats him to death with a sledgehammer. With police attention mounting, he begins moving on to Curtis' closer friends and loved ones, electrocuting his on-and-off sexual partner Therese, reducing his therapist to molten sludge, and throttling Trevor (Curtis' close friend and almost-lover) to death with extension cords - though somehow, Jocelyn (his "official" girlfriend) manages to escape unharmed.
Fortunately, though driven to the brink of madness and in imminent danger of being arrested for murder, Curtis is able to follow the trail of clues into the Threshold project hidden under the Wyntech building. Here, a gun-toting Warner informs Curtis of his true nature and the fate of the real Curtis Craig - before the Hecotomb appears and tosses him aside. Unable to appeal to his other self's sense of mercy, Curtis flees through the portal into Dimension X.
After a difficult journey through the alien landscape, he eventually discovers the real Curtis Craig's body, still cocooned in the Threshold-Dweller's life-support systems. Enraged at having his deformity revealed to the clone, he unleashes one last psychic attack on Curtis in an attempt to seize his mind: over the course of the mental battle that follows, Curtis is threatened with vivisection at the hands of Dr Marek, has a gun held to his head by Jocelyn, is menaced by a trio of zombies consisting of Trevor, Tom and Bob, gets tortured by an electrokinetic Therese, before finally coming face to face with his abusive mother - now armed with a pair of gardening shears. However, Curtis is able to defeat every single scenario, finally defeating his real self's mental power when he convinces his mother to abandon her hatred.
With his powers exhausted by the battle, the Hecatomb can only watch helplessly as the clone disconnects his oxygen mask - revealing the real Curtis' face as he slowly asphyxiates to death.