Gillehspy served as a captain within the Galactic Empire's military, an Imperial officer during its initial period. He was in command of the Venator-class Star Destroyer known as the Hound.
Following Lieutenant Gregg's notification to Darth Vader regarding Dass Jennir's whereabouts on the Colonies planet called Kestavel, Vader instructed Gregg to have Gillehspy ready the Hound for departure within one hour.
While on a mission to Kestavel, and after receiving reports indicating that Vader's troops were ensnared in a trap involving engine fuel, Gillehspy, who was watching the combat from the vessel's exterior, tried to obtain additional details from the bridge. However, he was compelled to cease his inquiry at blasterpoint by Lieutenant Gregg, who, on Vader's previous orders, was to stop any interference with Vader's mission from Imperial forces, even assistance to Vader himself.