UrSu is Jen's master (the one who found him as a baby and raised him), and is also the counterpart of skekSo, the Skeksis Emperor. Before he died, urSu commissioned Jen for his quest, showing him what the Crystal looked like and where to find it - at Aughra's observatory. "UrSu the Master chose death that the balance of UrRu and Skeksis might be broken. Wise was he always and subtle in meditation beyond understanding." (The World of the Dark Crystal).