Cain was originally a senior member of the US military during the Civil War, and lead the Incarnates program with his childhood friend Captain Hank and genuis bioengineer Dr. Elaine Bluelake, with Bluelake being in charge of converting volunteer human soldiers into "Incarnates" (monstrous creatures with God-like powers and strength) in order to ensure their victory in the war.
After many successful missions, Cain came into Hank's tent to congratulate him and his Incarnate squadron on their victories. In fact, Cain had been ordered to wipe out all incarnates, as a peace treaty was underway and the incarnates would be unable to adjust to the modern world and likely become a threat to mankind. For this purpose, he ordered Elaine (who had already converted Cain into an incarnate of human appearance) to create several so-called godkiller bullets.
In Hank's tent, he informed him that Elaine had wanted to see him to "tell him something" (in fact, he had ordered Elaine to kill Hank simply to toy with her, as he knew that she was in love with him).
Outside the barracks, Elaine repeatedly apologised to Hank about having to kill him, but knew that it was the only way to protect humanity from the incarnates, so she shot him in the stomach and apparently killed him, just as Cain had ordered. She then handed the godkiller bullets to Cain, and told him that she would go on executing other incarnate members as he had instructed before she and Cain would kill themselves, destroying any possibility of the Incarnates being recreated. Hank initially thought that Cain was doing all this for Elaine, to prevent her from having a legacy of death and regret. These thoughts were proven false immediately when Cain turned his gun on Elaine, said "You two are the only ones who will die!", and shot her dead, before laughing hysterically.Having successfully unleashed the Incarnates upon the world, Cain went underground for a time, using his powers to manipulate and cause pain among others for his own amusement, while amassing an Incarnate army of his own and keeping it at his mansion. He resurfaced in the town of Whitechurch ten years later, when he and his young maidservant came to investigate sightings of his former underling Christopher Keynes, an incarnate who had come to resemble a gargoyle and become a serial killer operating out of the Whitechurch area.
Upon entering the town, his maidservant and he were propositioned by two prostitutes, and Cain initially accepted their advances, before staring into the eyes of one of the girls and using his powers to brainwash her mind into that of a ravenous beast driven solely by hunger. The brainwashed girl then attacked her friend and chewed her throat out, while Cain smiled, before becoming bored by the sight and walking off with his maidservant, declaring that a world with "dull evenings" like this make the world's existence utterly pointless.
Becoming the second serial killer in the town of Whitechurch, Cain set about finding the first and using him to draw out Hank (whom he had discovered survived Elaine's attack).Cain then met up with "Gargoyle" (Christopher Keynes) in the abandoned White Church, for which the town was named. He then supplied Gargoyle with one godkiller bullet for the sole purpose of killing Hank. After Gargoyle failed to kill Hank and was killed with a fatal headshot by Hank's travelling companion Nancy Schaal Bancroft (who was generally referred to by her middle name only), Cain and his maidservant suddenly appeared in the church to Hank and began toying with his emotions for amusement, causing Hank to shoot him in the head.
After being shot, black flames started emanating from Cain's bullethole, as his face healed itself completely. His underling Elizabeth Weezer, aka Arachne, (a giant human-spider hybrid-type incarnate) then revealed herself to have been hiding behind Schaal and Hank, identified Cain as being a "very special type of Incarnate", calling him "The Undead King of Blood and Night, before Schaal and taking her as Cain's hostage. Cain then invited Hank (under the presumptive threat that he would kill Schaal if he refused) to a formal party which would occur later that week at his manor house. Cain then bid his former "friend" farewell, before jumping from the window alongside his maidservant, and making his getaway, while Arachne scuttled away with Schaal.
At Cain's mansion, Arachne forcibly undressed Schaal and put her in a somewhat revealing but still formal dress for the gala. At the gala, Hank and fellow Beast Hunter Liza arrived at the gala with hopes of rescuing Schaal from Cain and discovering his true plans. While at the gala, one of its many rich guests asked Hank if he was another of Cain's beneficiaries, but before he could answer Cain himself appeared on the ballroom's raised stage, and gave a speech thanking his beneficiaries and elaborating on the economic effects of the Civil War and how it had hampered all of their estates, before carefully changing the subject to make it seem that no peace treaty should have been written, and that the morally right thing to do would have been to use the Incarnates to finish the war by completely obliterating all who rebelled, calling his former military commanders "Cowards who were just scared of the incarnates' might".
Cain then said "And now, thanks to everyone's support, preparations are complete", before releasing fog into the ballroom, which lifted to reveal that the room was filled with incarnates. Cain the declared that, having been given their money for his campaign, his beneficiaries were no longer of any use to him, and ordered the incarnates to kill them all, whilst he smiled, taking immense pleasure out of their horrific deaths. Hank tried to plead with Cain to stop them, prompting Cain to remind him that Elaine had said that "All incarnates eventually lose their humanity", before lecturing Hank on the true meaning of humanity as a concept, all the while arguing hat he hadn't lost his, all in order to try to convince Hank to join him in his plan to reignite the Civil War and create a new era dominated by the stronger form of humanity: The Incarnates.When Hank refused to follow any part of Cain's horrific plot, Cain revealed that Schaal's dress had in fact been made entirely out of Arachne's silk, and was still connected to Arachne's body. Arachne then dragged Schaal up onto the stage using the thread, while Cain promised to "steal away everything that binds you on this dreadfully dull evening", sensing that Hank had feelings for Schaal. As such while a horrified Hank ran towards the stage to try to save her, a smiling Cain pulled out a revolver from inside his coat and shot Schaal in the stomach, after which Arachne dropped her to die on the floor.
Losing control of his abilities at the sight of Schaal dying, Hank transformed into his white wolf-like incarnate form, all the while Cain egged him on to give into his "true nature", this time going further into his transformation than he ever had since the Civil War ended, becoming too big to be contained by Cain's mansion, destroying its roof. At the sight of what he'd done, Cain started laughing hysterically, before shouting to his army "Behold, you stand before Hank, Lord of the Beasts!"
Cain is an intensely manipulative individual whose way with words often leads people to believe that he should be viewed as the victim of his circumstances and brings him many allies. His true nature is far darker, being extraordinarily sadistic even to those whom he claims to view as friends and has known for years, such as when he manipulated Elaine into shooting the man she loved before killing her out of spite. He has also shown that he is more than happy to turn on his own allies if they annoy him, or even if they simply lose their usefulness to him, irrespective of whether or not the fully support his goal, and his frequent smile while killing demonstrates the true depths of his sadism. He is also exceedingly arrogant, especially since becoming an incarnate, flaunting his inability to die by getting as close to his foes as possible and mocking the futility of their attempts to stop him.
Cain is also frequently bored, even quickly becoming bored by his own actions, and his boredom caused him to develop quite a nihilistic worldview, with him even saying at the end of vol.1 that "a world as boring as this does not have any point in existing". His nihilism is also demonstrated during his speech to Hank before killing Schaal, where he says that nobody had any right to judge the humanity or morality of others, believing that morality is a pointless mental construct, and anything that started off as human and remains alive will never truly lose its humanity, because it is biologically human.