Slayer of the Lifeless

Source
This item drops from Gluth and Gothik the Harvester in the 10-man version of Naxxramas.

Trivia
The item name and flavor text is a reference to the South Park episode "Make Love, Not Warcraft", in which a griefer named "Jenkins" (in reference to Leeroy Jenkins), who has "absolutely no life" ("The Lifeless") repeatedly kills the characters of Stan, Kyle, Kenny and Cartman. With aid of the Sword of a Thousand Truths (which has the same model as this weapon), they kill the griefer, as was foretold by "Salzman from Accounting".

This sword also shares the same model and icon as The Hungering Cold that dropped from Kel'Thuzad in Naxxramas.