Sure. I know some stuff, but it's all vague.
~Hit me with your best shot~, Riker.
Before God created humans and the other angels, he had made the Archangels and had a sister, who was called Amara but known simply as The Darkness. God and the Archangels fought and defeated The Darkness because in order to create the universe on the scale God did, God would need to sacrifice his only kin. But, because of her power, The Darkness couldn't be killed, so instead God sealed her away in a prison called The Mark of Cain, which he put on Lucifer because that's who he trusted most. The Mark, because it contained The Darkness, corrupted Lucifer into hating humanity(most likely because The Darkness was sacrificed to make them).
Faster forward a few eras and Lucifer went to Earth. He twisted the soul of Adam's first wife, Lilith, making her the first demon ever. He also was speaking to Abel, who thought he was speaking to God, but Cain knew the truth. Cain pleaded with Lucifer to leave Abel alone and Lucifer promised he'd send Abel to heaven on two conditions: Cain would go to Hell and he'd have to be one that sends Abel to Heaven. Cain accepted and Lucifer placed the Mark of Cain on him, making him thirsty for blood. So Cain killed Abel and then killed himself with something called The First Blade, which was huge knife he made from a jawbone. When Cain died, he became a power kind demon called the Knight of Hell. Knights of Hell can only be killed by someone who has both the First Blade and Mark of Cain. So Cain trained several other Knights of Hell, but he eventually left them to live on Earth with a wife. They got mad and went to attack him, but he killed all except one: Abbadon. Abbadon managed to live by possessing Cain's wife. Because the Mark causes a deep thirst to kill, Cain stabbed through his wife to kill Abbadon, but she left the body right in time to survive. Horrified at killing his wife, Cain went into isolation.
Abbadon found a way to travel to the future and caused a civil war in hell because she was trying to take the crown from Crowley. In order to kill Abbadon, who was a serious threat, Crowley tricked Dean into going to Cain's house and getting the Mark of Cain himself. After killing Abbadon with the blade, they then had to deal with a rogue angel named Metatron. Metatron ended up killing Dean, but because the Mark of Cain resurrects whoever has it on their arm as a demon, so Dean came back as a demon.
