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.