Protector, serving as the flagship for Imperial Admiral Harkov, was a Victory I-class Star Destroyer.
Because Harkov played a role in developing the TIE Avenger, Protector was among the first vessels to be outfitted with these new starfighters.
The Protector fulfilled various roles, including acting as the command ship for Imperial Navy forces within the Sepan system during the Sepan Civil War. Rebel pilot Ace Azzameen discovered it was also escorting convoys transporting construction materials and equipment covertly destined for the Death Star II. The ship was involved in Harkov's desertion and managed to evade capture for a short time following the Admiral's death. Imperial forces eventually tracked down and engaged the Protector. Despite assistance from the Rebel Alliance, specifically the MC40a light cruiser Warhawk, several CR90 corvettes, Delta-class JV-7 escort shuttles, and one of Harkov's EF76 Nebulon-B escort frigates named Akaga, Maarek Stele led Imperial starfighter forces that ultimately destroyed Protector.
The Voyages of the VSD Protector, a holo-serial, presented an account (likely fictionalized) of the Protector's adventures. One of the stories recounted an encounter with a slivilith.
The computer game TIE Fighter provides the initial depiction of the Protector, describing and showing it in gameplay as a Victory-class Star Destroyer. However, in a cutscene during the Sepan campaign, the Protector is shown as an Imperial-class Star Destroyer, due to the reuse of footage from a generic scene showing a return to base.
The Complete Star Wars Encyclopedia from 2008 indicated that within the Expanded Universe, there were three distinct Victory-class Star Destroyers bearing the name Protector. The Empire operated two of them: this particular ship and another, a Victory II-class Star Destroyer, referenced elsewhere.