The Skeksis are a fictional species which act as the main antagonists in the The Dark Crystal franchise. The word "Skeksis" serves as both singular and plural form for this species. They are described by concept artist Brian Froud as, "part reptile, part predatory bird, part dragon". The Skeksis are represented by puppets engineered under the direction of Jim Henson. Jim Henson said that in the development of the Skeksis, the creators drew inspiration from the Seven deadly sins.

    The Skeksis are tall bipeds combining avian and reptilian features, wearing elaborate but threadbare robes of lace, velvet, and brocade to apparently conceal their aged and constantly decomposing bodies while appearing large and more intimidating. Their heads are beaked like a vulture's, while simultaneously sporting curved fangs. They have enlarged bellies and long reptilian tails, as well as curved quills on their backs. While having four arms like their urRu counterparts, the Skeksis have only one functional pair as the other were initially wing-like before they eventually withered and atrophied. Though skekMal is one of a few Skeksis to make use of his extra arms in The Dark Crystal: Age of Resistance. In an episode of the Netflix series, it is apparent that the Skeksis species may have either a triple urethra or three male genitals.

    Despite their frail appearance, Skeksis are physically powerful as skekUng mustered his strength to cut through solid stone during the 'Haakskeeka' duel while a provoked skekSil single-handedly slammed pilaster rock onto protagonist Jen.

    The Skeksis are the corrupt rulers of the planet Thra, having inherited it from their benevolent urSkek predecessors, and embody the knowledgeable, yet unrestrained aspects of the urSkeks' behavior. The Skeksis culture favors repetitive flamboyance, emotional pettiness, and a wasteful attitude toward life. Though they are capable of alliances, each acts only of self-preservation to the point of immediate betrayals to benefit their personal agenda. Despite their few numbers, the Skeksis form shifting political parties that stabilize the Skeksis society despite some causing friction among them, especially if the Emperor greatly favours one party over the others.

    Before the events of Age of Resistance, the Skeksis were divided into the Imperial Allegiance (skekSo, skekSil, skekTek) which oversee their race's continuation, the Tithing Allegiance (skekLach, skekOk, skekEkt, skekShod) who collect tributes from the Gelfling clans, and the Security Allegiance (skekVar, skekAyuk, skekZok) who command the Gelfling castle guard. But following the Garthim War and before events of the movie, the Skesis reorganize themselves into the Diplomatic Allegiance (skekSil, skekOk, skekEkt) who maintain the castle to the Emperor's liking, The Religious Allegiance (skekZok, skekShod, skekAyuk) who oversee daily routines, and Military Allegiance (skekUng, skekTek, skekNa) who oversee the Garthim.

    Due to the accelerated decomposition of their bodies, the Skeksis constantly attempt to prolong their lives by using the properties of the Dark Crystal itself. Their primary method is absorbing sunlight channeled through the Dark Crystal, its potency dependent on Thra's three suns. Another method is a form of acupuncture, in which power lines laid on their castle channels the planet's energy to them and feeds back noxious pulses, resulting in their kingdom's wasteland appearance. A third method is extracting the vitality from other life forms by exposing them to reflected beams from the Dark Crystal, a process that originally destroys the victims before it was refined enough to reduce them into nearly mindless drones which the Skeksis keep as slaves. The life force is collected in a liquid form that restores a Skeksis' youth and vitality, the Emperor eventually making law that only he can partake of it. Gelfling were originally used for this purpose until their near extinction with the Skeksis forced to use Podlings instead, with the youth inducing effects of the resulting elixir created from their life force lasting for a few seconds.

    The Skeksis have created the Garthim through grafting corpses which are then animated by the Dark Crystal, and bred the sentinel Crystal Bats.