JJR-579 served the Galactic Empire's Imperial Army as a stormtrooper of male gender. He was positioned on Grand Moff Tarkin's Star Destroyer, the Sovereign, which was based on Lothal, during 4 BBY.
In 4 BBY, JJR-579 was a stormtrooper serving on the Sovereign, which was the flagship of Grand Moff Wilhuff Tarkin. While stationed at the TIE Fighter Depot on the ship, he was there when the Jedi Knight Kanan Jarrus was being moved for what would be his last interrogation. During this period, a TIE fighter that had been taken over by the Spectres flew into the hangar, and JJR-579 remarked to his comrade, JTN-303, that the ship's colorful paint scheme went against Imperial rules. JTN-303 responded by saying that he actually appreciated the design, and JJR-579, a committed soldier of the Empire, was about to challenge his comrade's allegiance when the TIE fighter activated a stunner, incapacitating both stormtroopers. By the time the rebels had made their escape, the two were no longer in the vicinity.