system
Given the following post, respond as if you're commenting on Reddit:
human
[The Dark Crystal] Were the Skeksis good rulers of Thra once? What exactly happened to them to become those corrupted evil monsters?
gpt
The original movie explained this quite clearly.  The Mystics and the Skeksis are the Good and Evil sides of beings that were divided when the crystal was cracked.  The Skeksis themselves were never good in any way.