SkekSo had ruled the Skeskis since the split of the Crystal, and the division of UrSkeks. He was part of a political alliance with skekSil, skekAyuk, and skekEkt. In the early part of his reign, skekSo had shone with glory, leading feast processions and dances, beating all his rivals in tournaments. As the Skeksis aged and diminished, skekSo kept authority through favoritism, suspicion, and sheer courage. But soon his sight weakened, his body rotted with ulcers, and the other Skeksis awaited his death.
Production notes for the film emphasize the Emperor's dying face "going dark like a piece of bad fruit", as opposed to Master urSu turning into light. For the final deterioration of skekSo, a puppet was made of a wax with high melting points so that it would crumble and melt away at different rates. Skeksis decompose so quickly because they have no soul to slow the process.
|“||The Skeksis joined nothing except to make new combinations of evil. SkekSo the Emperor in the first days of his glory proclaimed otherwise; he held court not only over the Skeksis but over many Gelfling that went to serve in the castle. They shone in his glory; they carved and sang and painted and danced from the pleasure of the court. On all the days of feasting the Emperor led the processions and the dances of life and pleasure; his voice heard above a multitude; and always in the tournaments he bore down all rivals. In those days the Skeksis were still radient with energy, never still. But that radience diminished as their true nature showed and worsened; none was more terribly changed than the Emperor. His power he kept till the end; no other Skeksis held ascendancy other than through skekSo's favor, easily withdrawn. But his vigor lessened, his suspicions grew, his sight weakened, ulcers burst from his skin. He sought elixirs and enchantments to restore his rotting body, never more than a few days success. All awaited his death; his courage never failed.||”|
Although no performer is given a puppeteering credit for the Emperor in the film's ending credits, it can be inferred, based on information given in The Making of the Dark Crystal, that Jim Henson performed skekSo: "A few leading roles had been assigned well in advance of shooting. Jim Henson would enact Jen, the dying Emperor, and the Ritual-Master."