World of Darkness is a suite of tabletop role-playing games released by White Wolf publishing. The titles tend to be recognizable by their format: “[Noun]: The [Other Noun].” The most famous of these is Vampire: The Masquerade. They are set in a fantastic version of the modern world that is inhabited by vampires, werewolves, mages, and so on, all of whom prey on or interact with fairly oblivious humans.
New World of Darkness was a revamp of the original, incorporating a new rules system and tone: specifically avoiding the previous gothic feel for a more traditional form of horror. More specifically, the new version has the supernatural as less omnipotent and the setting as more unified, both for game balance and flavor reasons.
The World of Darkness has developed something of a reputation among role-players due to extremely strong player characters and questionable balance choices, leading to power-gaming. White Wolf employees are known to play God Mode Sues at events, behaviour generally disliked by the player base. In the old version of World of Darkness, this was compounded by a tone actively drawn from Anne Rice and more maudlin works of vampire fiction. The upshot is that fanfiction set in this universe tends to center on wangsty God Mode Sues.
Agents should note that new and old World of Darkness, while drawing on largely the same premise and source material, are independent continua. Likewise, the two computer games associated with the World of Darkness (Vampire: The Masquerade: Bloodlines and Vampire: The Masquerade: Redemption) should be considered as further sub-continua.