Text from The Making of the Dark Crystal by Christopher Finch
Jen
Raised by the Mystics in their valley, Jen believed that he was the last survivor of the Gelflings, a race of fawn-like elfin creatures. But when his dying master sent him on a quest, he discovered he was not alone. The Dark Crystal is the story of the terrors and final triumph of Jen's quest.
Like Jen, Kira survived the slaughter of the Gelflings. Rescued by the Pod People, she learned to live in harmony with the woodland creatures who inhabited the swamps and forests surrounding the Pod Village. When fate brought Kira and Jen together, she joined him on his quest. They gave each other strength, encouragement, and the will to succeed.
Old enough to know the world that existed before the race of Gelfling came to be, Aughra remembered life before the Mystics and Skeksis evolved their separate codes. She studied the movements of the planets in the heavens and lost an eye a thousand years earlier observing the last Great Conjuction of the Three Suns. Jen was sent by his master to Aughra to fulfill the prophecy and find the shard that would make the Crystal whole again.
When at the instant of the last Great Conjunction, the urSkeks were divided into two races, it was the Mystics, or "urRu", who took on the sorrows of the world. Although they had inherited the mystical wisdom of the urSkeks, they were powerless to use it outside their own valley, since the division had robbed them of the ability to act. Their hopes for redemption rest on Jen.
For every Mystic there was a corresponding Skeksis. SkekTek the Scientist was the counterpart of urTih the Alchemist. Skek Ayuk the Gourmand was the alter ego of urAmaj the cook. 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.