Skeksis

"For every Mystic there was a corresponding Skeksis... The Skeksis had control of the castle where the Crystal was kept; in its chamber they practiced their evil arts, hating each other as much as they hated the rest of the world."
 * - The Making of the Dark Crystal

When the Crystal cracked, one of the two races resulting from the split were the evil Skeksis, embodiments of the evil inside the UrSkeks. Possessing all of the negative attributes of society, and none of the positive ones, they live out a superficial existence of intrigue and plots against each other while struggling to retain their grip on Thra. They keep essence-drained Podlings as slaves, have their own personal army in the Garthim, and absolutely despise Gelflings, a race they think they have completely exterminated.

In The World of the Dark Crystal, Jim Henson commented that the Skeksis were based on the Seven Deadly Sins, but that since there are ten Skeksis and only seven deadly sins, they used some sins twice and made some more sins up.

The Skeksis

 * skekAyuk the Gourmand
 * skekEkt the Ornamentalist
 * skekNa the Slave-Master
 * skekOk the Scroll-Keeper
 * skekShod the Treasurer
 * skekSil the Chamberlain
 * SkekSo the Emperor
 * skekTek the Scientist
 * skekUng the Garthim-Master
 * SkekZok the Ritual-Master

Cultural references

 * A verse of the Scissor Sisters' song "Return to Oz" makes reference to the Skeksis as a metaphor for drug-absuing rave-goers.
 * A season ten episode of South Park features a "Nanny Skexis" who sounds like Chamberlain.