This knife originally belonged to [[Ruby]] and is capable of destroying most [[demon]]s if the stab wound is in an immediately fatal place, such as the neck or heart. Killing demons with the knife comes at the cost of killing their human hosts at the same time unless the vessels are already dead when they are possessed. When stabbed in less vital areas with the knife, the demon experiences intense agony but survives.<ref>[[4.10 Heaven and Hell]]</ref><ref>[[6.20 The Man Who Would Be King]]</ref> Its blade is inscribed with symbols and the handle is made from either wood or bone. Of all the demons that have been stabbed with the knife, only [[Knights of Hell]] such as [[Abaddon]]<ref name="eight12">[[8.12 As Time Goes By]]</ref> and [[Cain]]<ref>[[9.11 First Born]]</ref> and [[Princes of Hell]] like [[Ramiel]]<ref>[[12.12 Stuck in the Middle (With You)]]</ref> have been shown to be immune to its killing power. [[Alastair]]<ref name="four09">[[4.09 I Know What You Did Last Summer]]</ref><ref name="four16">[[4.16 On the Head of a Pin]]</ref> was stabbed in the left shoulder both times, although both stabs were very close to his heart. [[Bobby]] is the only known person to survive being stabbed with the knife, having stabbed himself to kill the [[demon]] possessing him at the time,<ref>[[5.01 Sympathy for the Devil]]</ref> but the knife left him paralyzed from the waist down.<ref>[[5.02 Good God, Y'All]]</ref> It also has no effect on [[angels]],<ref>[[4.01 Lazarus Rising]]</ref> but it can kill [[hellhound]]s if the wounds are fatal.<ref name="eight14">[[8.14 Trial and Error]]</ref>
The knife is "an ancient demon-killing knife of the Kurds" described by [[Henry Winchester]].<ref name="eight12"/> How Ruby was able to come across it before she met Sam is unknown.