Samhain saved Cassie Hack from the Black Lamp Society murder attempt. He has no memory of his past life except from his exceptional fighting skills and his hatred to the Society; he also remembers none of his past killings and his attempt at murdering Cat Curio. Maybe because the Society killed the one person important to him. He's trying to rescue Ava Park from the Black Lamp Society with the aid of Cassie and Vlad.
He made his first debut in Hack/Slash: The Series #20 Samhain is a jack-o-lantern masked ex-slasher, called a "Paladin" by the Black Lamp Society. When Cassie was being sent to prison, the Society members stopped the van and attempted to murder her for being a daughter of Dionysus. He killed the members who tried to kill her and left her change to call for help. His conscience restored as well as his lack of desire to commit meaningless murder like other slashers.
In later issues, Samhain's face is revealed from behind the mask, he's shown to be muscular, handsome young man with black hair and blue eyes. In Hack/Slash: The Series #24, he revealed the origins of the Black Lamp Society. That the Black Lamp Society followed the teachings of an alchemist
Akakios who believed that humanity was divided into two breeds. The first one was the superior one, with a strong sense of morality and a higher level of intellect. The second one, prone to sin and debauchery. This class was known as the "Children of Dionysus" as they were fond of wine and the seek of pleasure. During one of his journeys to Africa, Akakios destroyed a tribe that he discovered who used a rare plant to create a mysterious elixir.
The plant created a black flame when burned and when injected into a corpse, it allowed the dead to come back to life. However, Samhain explains that Akakios and the Society abused the plants' properties. They used it to allow the believers to come back to life and punish every non-believer lower human being and ensure their corrupted vision of a perfect world. He also reveals to Cassie, that while the bloodline has thinned through the decades, the Slashers, including her mother the Lunch Lady, and Cassie herself, were those who had part of the plants properties in themselves. Meaning that because of the black ambrosia, it meant Cassie had the potential to be a slasher like her mother.
Vlad didn't like what Samhain was saying nor did he like that he was basically implying that Cassie would someday end up like her mother. While she didn't like or believe half of what he was saying, she agreed to help Samhain find and rescue his lover, Ava Park. When they reach the Cedar Island Reserve, they are ambushed by creatures called the Artemis, some form of human-beasts created by the Black Lamp Society. While the trio fight desperately, they are almost completely outnumbered and are too powerful to destroy. During the struggle, one of the Artemis drugs Samhain, and he's dragged back to the lab in the mansion.
Samhain is captured and reprogrammed to be a Slasher once more, by one of the Society's leaders. And his first target is his own lover, Ava. While he does try to resist, he can't and slashes Ava. Ava, wanting to be free of the leader's influence, begs Samhain to finish her, which he does. But not soon after, Cassie and Venus (another one of the Society's creations, meant basically to be a sex slave) try to come and snap him out of it. While the leader goes after Venus, Cassie and Samhain are left fighting one another, since Vlad is still fighting off the Artemis. However, a passionate kiss from Cassie breaks his brainwashing. Together they eliminate one of the Society's leaders and escape.
As the whole group leaves, the island burns, due to it being triggered to die when the leader does. The group swims away from the island back to where the van is. As Cassie, helps dress Venus, she asks what will become of her and Samhain. Venus explains, they plan to try and shut down any labs or operations of the Black Society. Knowing the society has tried to kill her, Cassie offers to always be of help if they need her. Before parting, Samhain tries to thank Cassie for the kiss and try to make sure nothing is mixed up with feelings.
Cassie calmly tells him it was only to wake him up and not to worry. But for Cassie, this also awakens something inside of her she didn't think possible, and in later issues is found to be deeply fantasising and desiring this masked man. Samhain's feelings are not yet known, for the most part it may be one-sided. Later on in an issue, he and Venus (now calling herself Ava) are shown to be in a sexual relationship. Its unknown if the two really loved each other, as Venus/Ava admits to Lisa during a discussion, that whether physically or emotionally men are unfaithful.
Samhain and Ava arrived at Lisa Elsten’s animal shelter, not knowing they were being followed by Cat Curio. Mostly, Cassie had requested the two, to keep an eye on the couple for their safety. With influence from the Black Lamp Society, the heroes would soon have their hands tied. Cat, Chris Krank, and sheriff Maggie Reilly, would be fighting off an undead army of animals by the also resurrected Bobby Brunswick. During this battle, Samhain saved Ava from a pack of zombified animals, but having full memories of him being the one who put her in the coma she was afraid of him. While Cassie and Vlad fought off a resurrected Acid Angel.
But as for Cat and Samhain, there was no time for confrontation as more came. The group would have to rush back to town, as Lisa had been left alone, unprotected. Maggie Reilly soon left the group's side; unknown to the group that she was a member of the Black Lamp Society. Cat and Chris had been delayed as they had to save Ava from Bobby's zombie aquatic pets, and met up with Pooch for help in their battle.
Samhain able to fend off Bobby, before he could do any injury to Lisa and her unborn baby. During the struggle, Bobby refers to Samhain as his father and his god. When Maggie returns to help, she dies protecting Ava. But she also warns Ava that Samhain is really Akakios, the founder of the Black Lamp Society and that he's dangerous. Ava uses the oil to burn and kill Bobby, but she warns Samhain to leave or she'd do the same to him. When he becomes forceful on her, to know what Maggie said, he leaves shaken by his own actions.
Since then Ava now wants nothing to do with him and won't even say his name. With help from Cat, Cassie eventually finds Samhain and confronts him about what happened. He admits he ran, but not because of seeing Ava in pain. He left because he followed Cassie and that he felt an attraction too. Her kiss helped him regain himself once and hoped she could again. The two kiss but Cassie admits she needs him more now as an alley.
While Vlad was laid up with an unrevealed illness, Cassie brought in Samhain to help her defeat Bomb Queen and other escapees from the Interdimensional women’s prison. Bomb Queen also sensed a great darkness within Samhain.
Searching for a cure for slashers and the darkness within Samhain, Cassie and Cat took him to Doyle Valley in South America. After a dangerous procedure, Samhain was cured of his darkness and he and Cassie consummated their relationship. But it would be short lived when he's gravely injured, during a battle with Psychosaurs. Whether to save Cassie or help her, he knows he can't now that he's mortal. He manages to free one of the doctor's from their control. In return, he regretfully asks for the doctor to return him back to what he was, a slasher controlled by darkness.
He's force to try and control all his dark urges again. Before he can, the Psychosaurs attack again and unknowingly bring out his true side as Akakios showing he's killed for over decades and shows a brief memory of him founding the society. Though he does save Cassie and Cat from their encounter with slasher Buck Kemp, the reunion's short lived.
As Samhain is still consumed by the darkness (or his Akakios personality) and stabs Cassie. Before he goes to attack Cat, Gorillaconda slaps him a good far distance and takes them to Dr. Carpenter (the doctor Samhain saved) to treat Cassie. As Cat gets ready to lure a spider beast away from Cassie, she's stopped by Akakios/Samhain. He reveals that he sees himself as a cure for all diseases and could have gone purifying the world. But a sorceress had stolen his memories, and with his memories gone he had become a paladin. As Samhain, he was a blank slate, trying to find a purpose, and thought even love could free him. Akakios sees the world will belong to him now.
After another failed attempt to reach Samhain, he and Cat are ambushed by the giant spider (after its killed Gorillaconda). His weight ends up crushing the bridge they were on and they fall. But Cat is caught by the last minute by Cassie, however, Samhain is holding onto Cat's leg. Though its not known if Sam, was still there or if it was Akakios still in controlled. Either way, he tried pleading again to Cassie, saying she could still save him.
Although it hurt her to choose, Cassie saw she couldn't take the chance. To save Cat, she shot Samhain in the head and let him fall. Eventually his dead body showed up in South America. He soon resurrected when a jaguar bit him.