|“||It's called the "Mark of Cain" for a reason! First...first, you'd kill Crowley. There'd be some strange, mixed feelings on that one, but you'd have your reason. You'd get it done, no remorse. And then you'd kill the angel, Castiel. Now, that one...that I suspect would hurt something awful. And then! [...] Then would come the murder you'd never survive, the one that would finally turn you into as much of a savage as it did me. [...] Your brother, Sam. The only thing standing between you and that destiny is this blade. You're welcome, my son.||„|
|~ To Dean, "The Executioner's Song"|
He is portrayed by Timothy Omundson, who also plays King Richard in Galavant.
Cain and his younger brother, Abel, were the first sons of Adam and Eve, and the direct ancestors of Sam and Dean Winchester. Cain loved his younger brother deeply.
One day, Cain found Abel talking to some unseen force that Abel claimed was God. Cain, however, found out that his brother was really talking to the Archangel Lucifer, who sought to corrupt Abel. Wanting to save his brother, he made a deal with Lucifer in which he exchanged his own soul in Hell for Abel's in Heaven. Lucifer slyly agreed, but added the catch was that Cain had to kill Abel so Abel could go to Heaven. Cain therefore killed him, using an animal's jawbone (which became the First Blade), marking his legacy as a killer and "the Father of Murder."
Lucifer, in response, gave Cain a supernatural mark, which came to be known as the Mark of Cain, that empowered him greatly but also corrupted him. Unable to take the strain, guilt, and pressure of the Mark, Cain committed suicide but, due to the Mark, instead of dying, his soul was transformed into a demon, making him a Knight of Hell.
All future humans believed Cain to be pure evil and nothing less than a demon, but although Cain did become a demon when he died, Cain was in fact trying to save his brother from going to Hell.
Cain returned to Earth and led the Knights in destroying and butchering. He was, however, still remorseful about his brother's fate and wanted to be human again. In the late 1800s, Cain met a woman, Colette, and fell in love with her. He explained to her that he was a demon, but said he had saved his brother from Lucifer. Colette forgave him for all his sins and thus managed to draw him away from the life he had been roped into.
However, feeling that Colette was leading Cain astray, the Knights of Hell kidnapped Colette and had Abaddon possess her. Furious at what they had done, Cain picked up the First Blade and slaughtered all the Knights of Hell (and all the demons helping them), leaving him even more feared by all demons. He finally found the last one, Abaddon, who was still inside Colette. Abaddon first tried to convince Cain to return to them, but when he refused, taunted Cain about his failures and humanity, then began slowly killing Colette. Enraged, Cain stabbed her, but Abaddon vanished just before, causing Cain to accidentally kill his own wife. Before Colette died, he apologized and promised her he would never kill or mix with demons again.
Over a hundred years later, Dean Winchester and Crowley were hunting for the First Blade to kill Abaddon (who was in the process of usurping Crowley's position as ruler of Hell), and their investigation led them to Cain's home. Crowley tried to get Dean to retreat from him but Cain teleported behind them and took them inside to talk. Now claiming he was retired, Cain revealed that he was well aware of they were Dean who was his direct descendant and Crowley, king of hell. Although initially reluctant to help, he denied giving him the blade, and told the two to leave. Meanwhile, one of Abaddon's followers managed to track them down and, realizing what they were dealing with, called in Abaddon's army before they progressed.
Dean and Crowley later broke into Cain's home to look for the First Blade, but Cain caught them. Just then, Abaddon's demons arrived. Using his powers, Cain kept them out, but also kept Crowley in, as he was interested in Dean. Cain tested Dean's skills by letting several demons in, and Dean managed to kill them, proving himself.
Cain then revealed what had truly happened all those thousands of years earlier and about Collette before revealing that he did not actually have the First Blade anymore. He did, however, have the Mark and offered it to Dean as, without it, the First Blade would not work. Dean took the Mark of Cain so he could kill Abaddon. Cain then asked Dean to kill him when he had finished because he was tired of immortality.
Cain then vanished and went to Collette's grave, where he apologized to his dearly-departed wife for what he was about to do before returning to his home, where he then opened all the doors and let Abaddon's army in. After banishing Dean and Crowley outside, Cain used his powers to trap the demons inside and then single-handedly killed every last one of them.
"The Executioner's Song"
Unfortunately, doing this caused Cain to lose control of the Mark's blood-lust. Falling after so many centuries, he became convinced that his own bloodline was cursed (it did have the majority of the murderers) and decided it was his job to clean up the mess. Unfortunately, as one of the founders of humanity, that meant he was going to wipe out 10% of the total population. Cain got busy, wiping out several bloodlines. He had gotten to the Tolliver line, killing Tommy Tolliver (a serial killer) and his father (another murderer).
He met the angel Castiel who found out where he was burying the bodies of his victims, and told the angel about his plans. Castiel tried to protest his plan, but Cain dismissed him, deciding it was for the best. He spoke to Castiel about Dean, having learned about him killing Abaddon and telling Castiel there was no cure for the mark since Cain was living proof of that. Castiel tried to stop him, but as Castiel wasn't a descendant of his, Cain just left.
Later, it was discovered that Tommy had a son, Austin; since Austin was the last in the Tolliver line, the Winchesters, Castiel, and Crowley knew that Cain would go after him. Dean was forced to ask for the First Blade back from Crowley, as it was the only weapon that could kill him; Crowley agreed, as Dean pretended that the King of Hell was on Cain's list.
Cain arrived and went for Austin, but paused to talk to Castiel, to whom he admitted not all the killers were his and not all of his line were killers, but as they made up the majority of humankind, this was for the best and Austin could go either way; as such, he was going to play it safe. Castiel tried to stop him, but the angel proved no match for Cain, who effortlessly defeated him.
Teleporting into the barn, Cain realized he had been tricked and Austin was an illusion. Recognizing it was magic, he predicted that Crowley was there, then guessed that they had trapped him in a devil's trap. He casually congratulated the Winchesters and Crowley before warning them that it wouldn't hold him for long. They told him it didn't matter, and knowing that Dean was there, Cain asked if he was okay.
Armed with the First Blade, but in danger of losing himself, Dean confronted Cain. The two men talked shortly, with Cain admitting that he had honestly considered giving up and letting Dean kill him when he talked to Castiel; however, he knew if he played along, then Dean would bring him the blade. Dean tried to kill him, but Cain proved to skilled and kept knocking Dean around, the devil's trap barely containing any of his powers.
Even with the Mark's enhancements, Dean was out of his league; Cain, however, figured he was holding back due to fear of losing himself. He told Dean it was impossible not to, and he (Cain) was living proof of this. Overpowering the hunter a final time, Cain took back the First Blade and, feeling its infernal power, took Dean down, planning to kill him.
He admitted to Dean that he really did care about him and explained that Dean was doomed to lose control of the Mark just as he himself had, and would eventually murder Castiel and then Sam, the latter of which would destroy him and leave him a monster; as such, by killing Dean, Cain was sparing him from this fate.
However, at the last minute, Dean managed to grab Cain's own sword and cut his hand off, separating him from the First Blade. The shock of this allowed Cain to regain control. Kneeling before Dean, Cain accepted his fate. Dean took back the First Blade and, before killing him, begged Cain to tell him that it wasn't necessary and there was a way back. Cain told him there wasn't, so Dean sadly fulfilled his promise and killed Cain, giving him the death he had wanted for so long.