User blog comment:NaiflidG/Discussion on Cain (possible spoilers)/@comment-3045936-20131222212107/@comment-11331875-20131222224649

Oh, that's another possibility, TwilightDespair. Perhaps he was a cold-blooded murderer in life who was rejected by Heaven and sent to Hell, where he became a demon who later ended up feeling love for someone and feeling regret for his past and trying to redeem himself. I'm still not happy with the idea of a demon who retired for love, but I do sort of like the irony of that.

Maybe, General, Azazel was another condemned sinner. From what I remember of the Biblical Azazel, he was one of the angels who mated with women and produced the nephilim, and taught humans the art of war or something, right? Perhaps Supernatural's version of Azazel started out as a human who either was a very brutal soldier, a rapist, or both. Either way, he was not someone Heaven would let in. Lucifer, thinking he was an example of the evils of humans, turned him into a demon. Since there's no demon named Samhain in real-world lore, I don't have much to twist into crazy speculation on Supernatural lore, but... considering his behavior, his control over monsters and spirits, etc., perhaps Lucifer created him to show how humans are nothing more than evil beasts, and that gave Samhain a connection to other beasts and allowed him to subjugate them to his will? That's the best I can come up with. Alastair... he was partially named after Aleister Crowley, A.K.A. "the wickedest man in the world," so maybe he was another sinner who went to Hell of his own actions or maybe he sold his soul to learn witchcraft (A.C. was an occultist). In Greek and Roman mythology, Alastor was a mortal who (along with most of his family) was killed by Hercules and became a demon as a result--he's linked to family feuds and particularly vengeance, doing things like punishing a person's children for the parent's crimes if the parent dies before Alastor gets ahold of him. So, twisting it around, perhaps Alastair in life murdered his family and went to Hell for it, or wrongly punished someone for something someone else did? Maybe he was a judge or something, and gave out bad sentences?