Cain was the firsborn son of Adam and Eve, the first human born, and the older brother of Abel. Although it was originally and commonly thought that Cain was jealous of his brother Abel, and killed him out of rage and contempt, Cain later revealed that Abel was in fact talking to Lucifer, not God as formerly thought. In an effort to protect his brother from corruption, Cain offered Licifer a deal. Cain offered himself to Lucifer so that Abel would go to Heaven instead. Lucifer agreed, on the condition that Cain himself would send his brother to Heaven. Thus, Abel was struck down by Cain using the First Blade, which he created from the jawbone of an animal.
After this, Lucifer branded Cain's right arm with the Mark of Cain, binding him to the First Blade.
Life as a Demon
After killing his brother, Cain descended into Hell and became a high-ranking demon soldier. He was considered to be the most terrible demon to ever walk the Earth before suddenly vanishing[1]. This act of killing between brothers would set the precedent of their descendants being the vessels of Michael and Lucifer, and thus, again require a brother killing a brother during the Apocalypse[2].
Cain hunting down demons in 1863.
Cain was the founder and mentor of the Knights of Hell. He created the entire order with his bare hands, and also killed all but one with the First Blade.
In 1863 in Jasper Springs, Mississippi, Abaddon, the last remaining Knight, possessed Cain's wife Colette, in an attempt to coerce Cain to return to his work as the leader of the Knights. When Cain declined, Abaddon killed Colette. It was during then Cain made a promise to a dying Colette that he would retire from his work as a Knight.[3]
During Cain's disappearance, all other demons thought or hoped he was dead. Crowley described him to be "the best at being the worst."
21st Century
Cain lived his life alone, and was a bee collector in Missouri. He met Dean and Crowley when they came looking for the first blade to kill Abaddon. Cain was initially unwilling and sent them away, warning them not to return. Never the less still searching for the blade, they broke back into his home. But where caught when Cain returned. Meanwhile multiple other demons showed up. Interested by Dean, Cain tested him and forced him to live up to his reputation, Cain realized that the hunter and himself were similar. Going back to his wife's grave, just as the demons forces were advancing Cain decided to transfer the Mark of Cain to Dean who excepted. Cain. He then teleported Dean and Crowley to safety after making Dean promise to return and kill him after killing Abaddon. He then took on an entire army of demons single-handedly and massacred them[4].
Personality
Unlike most demons Cain still possessed a good deal of his humanity and was one of the few demons to show love. He dearly loved his brother Abel, willingly becoming Lucifer's soldier to save Abel, and personally murdering him so that Abel would get into Heaven. He spent thousands of years doing terrible and brutal things with the knights. However he fell in love with a woman named Colette, who loved him even after she found what he was. This apparently restored most of Cain's humanity. Following his love dying because of Abaddon, Cain gave up his life of violence in a promise to her, and buried his head declaring himself retired.
By the time Dean came to him looking for the First Blade, Cain was living an isolated life like a normal man. And showed a passion for bee's. Initially seeming apathetic and uncaring towards Dean. Cain refused to help, but once Dean proved his strength Cain agreed to return partially to old ways, but apparently tired of life and what he was going to do, he asked Dean to kill him once Abaddon was dead, showing a death wish.
Cain also had an interest in Dean Winchester, having despite being retired heard a lot about him. He considered Dean and him to be very alike and was impressed to see Dean lived up to his reputation. He eventually agreed he was worthy of taking the Mark of Cain, making him the one to kill Cain.
Cain also showed an affinity for bees, taking up beekeeping after retiring, he considered them noble creatures.
Powers and Abilities
Cain is an extremely powerful demon. His reputation alone made Crowley reluctant to go anywhere near him, opting that he and Dean go "a world away" from Cain as possible. He could kill other demons with a mere touch. He could even prevent Crowley, the King of Hell and a powerful demon himself, from escaping and speaking just by a simple gesture. His strength was also shown when he killed an army of demons single-handedly.
Immortality - Being one of the original humans as well as one of the original demons, Cain is at least 180,000 years old. He hasn't aged since well before 1863.
Demonic Possession - He possesses humans to exist on Earth. He had been in the same vessel for over a hundred years.
Super Strength - Being the original Knight of Hell, Cain is considerably stronger than lesser black-eyed demons, casually overpowering and lifting one off his feet with one hand and snapping his neck with very little effort.
Telekinesis - He could move objects by snapping his fingers.
Teleportation - He teleported from across a field to beside Dean and Crowley and then to Collette's grave and back.
Cain uses his unique demonic smiting on a demon.
Demonic Smiting - He can kill demons with a touch similar to angels. Except in Cain's case, the color is red rather than bright white light.
Invulnerability - Cain is invulnerable to normal and mortal harm.
Apporting - Cain was able to teleport Dean and Crowley outside with a touch.
Power Negation - Cain is able to negate abilities of weaker beings as he did with Crowley, trapping him inside and stopping him from teleporting away.
Demonic Control - Cain was able to strip Crowley of his ability to speak with a simple gesture.
Spell Casting - Cain was able to non-verbally enchant his house so Dean and Crowley couldn't leave, or the other demons couldn't teleport in. He could undo and recast this spell with a snap of his fingers.
Trivia
The set for Cain's home is the same as Bobby's.
Cain is the first and only demon to display the ability to smite.
Cain is similar to Dean in many ways. Both of them wanted to keep their younger brothers from being corrupted. They also took extreme measures to make sure their brothers were saved, regardless of the rest of the consequences. Cain also remarked that Dean's bravery was very much like his. Finally, they both carried the same bloodline that could host the archangels.
Cain showed a considerable amount more humanity then any other demon, this is possible because he made the agreement to become a demon out of love towards his brother.
