Harbinger, a Star Destroyer belonging to the Tector-class, served the Imperial Navy during the era of the Galactic Civil War. This vessel was the only Tector-class ship in the Imperial fleet tasked with defending the DS-2 Death Star II Mobile Battle Station above the Forest Moon of Endor in 4 ABY. The Rebel Alliance was baited into attacking the ostensibly unfinished battle station by Emperor Palpatine, which led to the Imperial fleet cornering them above the moon. Once the Alliance engaged the Imperial ships, the rebel freighter known as the Millennium Falcon was observed flying across the hull of this Star Destroyer. However, following this initial skirmish, the Harbinger met its end at the hands of advancing Alliance warships, shortly before the destruction of the Death Star and a large portion of the Emperor's fleet.
The Star Destroyer Harbinger made its debut as an unnamed vessel in the background of the 1983 film Star Wars: Episode VI Return of the Jedi from the original trilogy. Its name was later established in "The Levers of Power," a short story penned by Jason Fry and featured in the 2015 book The Rise of the Empire.