Executive officer (shortened to XO), or first officer, was a position within the Galactic Empire's Imperial Navy. Nymos Lyle served as the executive officer to Admiral Rae Sloane on board the Imperial-class Star Destroyer Vigilance during the Battle of Endor.
- Catalyst: A Rogue One Novel (as XO)
- Thrawn (as first officer)
- "Bottleneck"—The Rise of the Empire
- "End of Watch"—From a Certain Point of View
- "The Levers of Power"—The Rise of the Empire (First appearance)