Ruby was introduced in the season 3 opener Magnificent Seven . At the beginning her true identity was a mystery. She killed a few demons with a special knife to save Sam, giving him the impression that she is a hunter just like the boys. At the end of The kids are Alright (3.02), she revealed to Sam her true nature - a demon. However, she continues to help and save the boys time and again in later episodes. Her background story was told in Malleus Maleficarum (3.09). Ruby was a witch who gave her soul to another demon and became one. When the boys opened the gate to Hell, she escaped. Unlike the other, she still remembers the time she was a human and told Dean that she wants them to win this war against the demons.Ruby is played by Katie Cassidy in Season 3. In season 4 the character appears in a new host, and is played by Genevieve Cortese.Ruby's true intentions were never clearly revealed until the season 4 finale (more on that later), but before those intentions were revealed, she seemed genuinely interested in regaining some form of humanity. Originally she was a sort of consultant to Sam and Dean in the ways of demon activity; and convinced Sam that she was also working to help Dean out of his contract that was going to send Dean to Hell. She even helped Bobby rebuild The Colt (a gun that can kill nearly anything, including most demons)After they were unsuccessful in freeing Dean from his contract and he was dragged off to Hell, her new mission was to help Sam kill the very powerful and very destructive demon Lilith. Sam, being infused with demon blood, had many super-human abilities, all to do with the mind (telekenesis, clairvoyance, etc.). Ruby began feeding her blood to Sam, almost vampiric in its manner, which began to enhance Sam's super-abilities. Due to these feedings, Sam was now able to exorcise demons back to Hell (in some cases kill them), just by concentrating hard enough. Sam was convinced that Ruby was enhancing his abilities for him to finally kill the demon Lilith. This was true...but not for the reasons Sam had thought.The Season 4 story arc was about the breaking of seals that would release Lucifer from his prison and allow him to walk the Earth once more. Ruby's true intentions were now revealed in the finale of this season. She did want Sam to become powerful enough to kill Lilith, but only because the death of Lilith was the final seal to be broken; she had been wanting to set Lucifer free the entire time, and she succeeded. However, despite succeeding, she was immediately killed afterwards by Dean with her own knife. Show less «