Scourge (Buffyverse)

The Scourge were the chief antagonists of the Angel episode "Hero" and are notable for being one of the few one-shot villains in a show to succeed in killing off a main character - in this case Doyle, who sacrificed his own life to stop their xenophobic quest to exterminate all "non-pure" species.

Story
The Scourge was an army of pure-breed demons bent on the extermination of every non-pure demon race on earth, as well as that of humanity itself. To this end, they sought to eliminate a group of Lister demons currently hiding in Los Angeles, intending to test their latest weapon, the Beacon- a device that emitted a light that destroyed anything with human blood that it came in contact with- on the Listers. Although Angel Investigations attempted to sabotage their attempts by having Angel infiltrate the group- claiming to loathe his 'half-breed' status- while they helped the Listers escape on a carge ship, the betrayal of the ship's first mate allowed the Scourge to get the Beacon on board the ship, the Beacon only being deactivated thanks to Doyle's sacrifice.

Trivia

 * The Scourge are very similiar to the Nazis as well as Supremacy groups such as the KKK
 * The Scourge also bare similiarities to Ken and his minions, the antagonists of the Buffy episode "Anne"