UrSu the Master was the leader of the Mystics following their split from the Skeksis. The kindest and gentlest Mystic, his counterpart was the wicked Skeksis Emperor. During the Gelfling genocide, urSu found an infant Gelfling being attacked by several Garthim. He drove the monsters away and took the baby with him back to the Valley of the Mystics. Here, he named him Jen and raised him as his adopted son. Jen in turned respectfully referred to urSu at all times as "Master."
In the ensuing years, urSu educated Jen in science, mathematics and writing, raising him into a bright and kindhearted young man. But as his counterpart, the Emperor, grew gravely ill, so too did urSu. As he lay dying in his bed, urSu sent for Jen. He told his adopted son of the Prophecy, instructing him to seek Aughra and find the Crystal shard. Only Jen could save their world, he opined.
Not long after this, urSu fell asleep and never awoke again. At the same time, miles away, the Emperor perished as well. UrSu's body gently faded from existence and disappeared, leaving behind an empty bed. A funeral was later held by his mourning fellow Mystics, conducted by urSu's close friend urZah, who presented his departed comrade with his personal possessions to take with him into the afterlife.