|“||Because demons can't be killed by run-of-the-mill cutlery. At the very least, you'd need an ancient demon-killing knife of the Kurds.||”|
The Demon-Killing Knife, or most commonly known as Ruby's Knife, is an ancient knife that was created by the Kurds which possesses the power to permanently kill most demons, hellhounds, and other demonic entities. Though it somehow came into the possession of Ruby, it eventually passes onto Sam and Dean Winchester, who use it as their one of their common means of killing demons besides angel blades.
At first glance, the knife appears to be an ordinary hunting knife with a curved, serrated-edged blade and antler handle (probably from some kind of deer). However, upon closer inspection, symbols can be seen engraved along the blade.
Powers and Abilities
This knife is capable of killing all but very powerful demons with a single stab to a vital area, such as the chest or the neck of the demons' vessels. As with the Colt, those killed by the knife briefly glow with orange light, which flickers out as the demon dies. Even non-lethal cuts are excruciatingly painful for almost all demons in the same way that non-lethal cuts from angel blades are to angels.
The knife is also capable of harming the Horsemen War and Pestilence; it was used to cut their fingers off in the episodes they appeared in. It is also capable of killing hellhounds. However, it is not capable of killing angels - aside from the damage to his vessel, Castiel was unaffected by the knife when Dean stabbed him during their first encounter. Its effect on other supernatural creatures are largely unknown, as it has almost never been used against anything else aside from a Rugaru in Purgatory.
The only subset of demons known to be immune to the demon-killing knife, are the Knights of Hell and Princes of Hell. White-eyed demons may be immune to it as well seeing how it was unable to kill Alastair and was never tested against Lilith however it has never been confirmed that Lilith herself was immune to it. Alastair could withstand several stabs from the Knife and found contact with it extremely discomforting rather than agonizing. However, the knife was capable of inflicting pain on the last surviving Knight, Abaddon; in fact, it was even able to temporarily incapacitate her for a few moments. It is unknown whether their resistance is permanent.  Even the first demon Lucifer created, Lilith, was said to be wary of it. Cain was the only one shown to be completely immune to the knife. Sam Winchester has implied that Samhain is too powerful for Ruby's knife to have the strength to kill the origin of Halloween, but Samhain seemed to refuse to face the knife directly in a fight. The Father of Murder did not flinch, wince, or show any pain at all when he stabbed himself in the heart with it. Dean's susceptibility to the knife was never tested, as while threatened with it, it was never used on him, though his complete lack of fear of it implies that, like Cain, it would be useless against him. Compared to Cain, the knife was able to harm Ramiel; in fact, the knife was unable to kill and injure the Prince of Hell, but like Alastair, Ramiel sprayed sparks out of the wound.
Creatures Affected By The Demon-Killing Knife
- Demons - Most demons with the exception of the Knights of Hell and Princes of Hell can be killed with the knife if stabbed in a lethal area. The White-eyed Demon Alastair proved to be durable to knife's demon-killing power. Sam Winchester believed that the knife could not kill Samhain.
- Hellhounds - Hellhounds can be killed with the knife.
- Horsemen - The knife cannot kill Horsemen but can harm them as shown when it was used to remove their rings.
- Rugaru - Rugaru can be killed with the knife as shown when Dean killed one with it in Purgatory.
- Dean Winchester
- Sam Winchester
- Bobby Singer
- Christian Campbell Demon
- Becky Rosen
- A member of Abaddon's Demon Army
- Linda Tran
- Guthrie (dream)
- Gunner Lawless
- Luther Shrike
- Mary Winchester
- Ruby's Knife (by everyone between Season 3-5)
- The Knife (by everyone as an abbreviation)
- Ancient Demon-Killing Knife of the Kurds (by Henry Winchester)
- Demon-Killing Knife (by Mary Winchester)
- Demon Knife (by Dean Winchester)
- Demon Blade (by Dean Winchester and Lilith)
- Series creator Eric Kripke originally wanted the knife's origins to remain unknown to retain an air of mystery. When Sam asked where she got it, Ruby deflected the question with a joke. Alastair did not recognize it, remarking that it was a "magnificent piece" and telling Ruby "you must tell me where you found it." However, the Season 8 episode As Time Goes By finally revealed that it was forged long ago by the Kurdish people, albeit with Kripke no longer as showrunner.
- Kripke refers to it as "a hand-to-hand version of the The Colt".
- Gluttony was the first demon to be killed by the knife on the show.
- A deleted scene from Frontierland shows the Colt's creator, Samuel Colt, was in possession of the knife in the nineteenth century.
- In a deleted scene from The Scorpion and The Frog, Luther Shrike examines the knife and states that the craftsmanship looks Kurdish. However, he doesn't recognize the dialect of the symbols on the blade. Sam claims that the knife is a family heirloom that he inherited from his "great-aunt" Ruby.
- Upon Sam and Dean obtaining the knife, they have used it readily to kill demons. However, in Season 9, the brothers more commonly use angel blades, possibly because they have a wider range of things to kill.
- In Season 10 the knife was only used to kill two demons in one episode. This is because contrary to previous seasons, demons are not a major enemy.
- Interestingly, the first of Lucifer's Knights of Hell, Cain is the only known demon, who is immune to both knife's demon-killing power and knife's demon-damage power. Alastair like Ramiel were durable to knife's demon-killing power as well, but the knife let both sprayed sparks out of the wound.
- When Sam attempts to use the knife to kill Crowley in The Prisoner, Crowley shows no fear, calling it a toothpick; implying it can't kill him. However, after Dean incapacitates him with an angel blade in Form and Void, Crowley seems nervous when Dean pulls the knife, indicating that it can in fact harm him.
- Interestingly, even though as the first demon, she is at the very least at the same level of power as the Princes of Hell and Alastair, Lilith has shown greater fear of the knife. A possible explanation could be that Lilith most likely couldn't be killed by it but it could still injure her like they proved able to be able to cause some pain on the Princes and Alastair and considering how Lilith never showed the same level of pain tolerance as Alastair, the knife could impair her to an extent.
- After the knife's introduction, there was a significant decrease in exorcisms. This seems fitting with the Winchesters' mentality of "shoot (or stab) first, ask questions later." In Our Little World, the Winchesters consider using an exorcism on a demon instead of the knife, but discover that the demon's vessel won't survive the exorcism due to a fatal wound and kill the demon instead.
- Sam and Dean are generally the only ones who use the knife. However, Ruby, Bobby Singer, Castiel, Meg, Becky Rosen, Gadreel, Linda Tran and Gunner Lawless have also used the knife briefly.
- In The Scorpion and The Frog, Sam calls the knife "very rare, one of a kind."
- Dean was the first person other than Ruby to use the knife.
- Both Alastair and Abaddon possesed a Resistence and Durability to Ruby's Demon-Killing Knife, and in the case of both, the knife was used to make very little time to escape from both powerful demons, and both were able to survive the stabbing of the demon-killing knife.
- In Season 13, the knife only appears in The Scorpion and The Frog as part of the Hunt for Barthamus' bones and is only used by Luther Shrike to kill Grab. Though demons appear throughout the season, the Winchesters use angel blades instead of the knife whenever they fight them.
- The knife is finally used by Sam to kill a demon again when he kills Kipling in Season 14's Stranger in a Strange Land. Notably, he chooses to arm himself with the knife instead of an angel blade like his companions. Previous to this, the last demon killed by one of the Winchesters with the knife was Ramiel's Protector by Sam in Season 12's Stuck in the Middle (With You). The last demon killed by Dean with the knife as of Stranger in a Strange Land is Marco in Season 11's Our Little World.
- After seeing the knife in Proverbs 17:3, Lilith calls it a Demon Blade. After seeing Dean with an angel blade immediately afterwards, Lilith comments that he "upgraded."
- In earlier seasons, the knife is generally called Ruby's Knife by the characters. Later  refers to it as an ancient demon-killing knife of the Kurds. It's referred to as just the demon-killing knife by Mary Winchester. Additionally, Dean calls it a demon blade  and explains to a room full of hunters that it kills demons, kills them dead. Dean calls it a demon knife when explaining to Gwen Hernandez how to kill a hellhound. Lilith calls it a Demon Blade upon seeing the weapon.
- Season 3
- Season 4
- Season 5
- Season 6
- Season 7
- Season 8
- Season 9
- Season 10
- Season 11
- Season 12
- Season 13
- Season 14
- Season 15
- Lazarus Rising
- What's Up, Tiger Mommy?
- As Time Goes By
- Stuck in the Middle (With You)
- As Time Goes By
- Michael Ausiello (August 19, 2009). "Ask Ausiello: Spoilers on 'Grey's', 'House', 'NCIS', 'Bones', 'Gossip Girl', 'Supernatural', and more!". EW.com.
- Knight, Nicholas, (Season 3 Companion), p.22
- As Time Goes By
- Stranger in a Strange Land
- Celebrating The Life Of Asa Fox
- Somewhere Between Heaven and Hell
- Proverbs 17:3