Goneril held the rank of adjutant within the First Order Navy, reporting to Captain Moden Canady. Their service took place aboard the massive Fulminatrix, a Mandator IV-class Siege Dreadnought, during the period known as the First Order-Resistance War. During 34 ABY, the dreadnought journeyed to the planet D'Qar, with the mission of obliterating the Resistance base located there. However, before the dreadnought could complete its objective, a Resistance X-wing starfighter, piloted by Commander Poe Dameron, initiated an attack, destroying the Fulminatrix's dorsal surface cannons. Goneril confidently asserted to Canady that the starfighter stood no chance of breaching the dreadnought's armor; a statement that prompted an irritated response from the captain, who pointed out that penetration was not the attacker's intention.
After the Fulminatrix ultimately engaged and destroyed the base, Goneril found themselves captivated by the resulting devastation on the planet's terrain. Goneril then informed Canady about the incoming Resistance bombers and the progress of the Fulminatrix's orbital auto-cannons as they recharged for another attack, this time targeting the Resistance's main capital ship. Not long after this, a successful bombing raid executed by the last remaining Resistance bomber resulted in the destruction of the dreadnought, leading to the death of everyone on board.
During the First Order-Resistance War, Goneril functioned as an adjutant within the First Order's naval forces. In 34 ABY, they were positioned on the Mandator IV-class Siege Dreadnought Fulminatrix, which, along with three Resurgent-class Star Destroyers, traveled to the Ileenium system in the Outer Rim Territories with the goal of eliminating the Resistance base on the planet D'Qar. However, upon the Fulminatrix's arrival over the planet, Commander Poe Dameron of the Resistance, piloting the T-70 X-wing starfighter Black One, diverted the attention of the First Order warships from firing on the base. Dameron then initiated an attack run on the Fulminatrix, detonating its dorsal surface cannons to render the dreadnought vulnerable to the Resistance's MG-100 StarFortress SF-17 heavy bombers.
After the Black One passed by the Fulminatrix's bridge to execute another attack on the dreadnought's cannons, General Armitage Hux of the First Order contacted the starship's captain, Moden Canady, holographically and demanded to know why the Fulminatrix had not yet destroyed the attacking starfighter. Goneril observed both Hux and Canady during their exchange. Following the captain's sarcastic response that their own fighters were needed to effectively defend against the X-wing—an action previously forbidden by Hux—he turned away from the bridge's viewport and moved toward the interior of the room. Goneril followed their superior officer, declaring that the attacker had no hope of penetrating the Fulminatrix's armor. Canady briefly imagined shoving the adjutant through a nearby airlock, before coldly replying that the X-wing's objective was to clear out the dreadnought's surface cannons, not to breach their armor. Goneril reacted with an incredulous expression, which Canady would have appreciated if their vessel wasn't in such a precarious situation.
Later, the captain of the Fulminatrix commanded the ship's orbital auto-cannons to open fire on the Resistance base. He then requested that the feed from the vessel's orbital imagers be displayed on a viewscreen. The resulting images showed a firestorm extending for kilometers across the planet's jungle from the site of the destroyed base. Goneril was mesmerized by the sight, standing motionless and staring at the screen with adoration.
Subsequently, as the Resistance bombers approached the Fulminatrix, Goneril informed Canady that the attacking ships would be within range momentarily. The captain then ordered the auto-cannons to be recharged and to target the Resistance's main capital ship, the cruiser Raddus. Warrant Officer Suday Bascus then reported that the auto-cannons were aimed at the new target, with Goneril adding that forty seconds remained until they were fully charged. Goneril was standing near another crew member's console when Canady gave the order to fire at the Raddus. However, at that precise moment, the last remaining Resistance bomber released its payload of proton bombs onto the Fulminatrix's dorsal surface, triggering a chain reaction of explosions within the vessel that ultimately consumed its bridge, resulting in the death of everyone aboard the warship.
Goneril was a human with light skin and dark eyes. They possessed confidence in the ability of the Fulminatrix's armor to withstand any assault from a T-70 X-wing starfighter, and the destruction inflicted on the surface of D'Qar by the Fulminatrix's orbital auto-cannons captivated Goneril and filled them with adoration.
Goneril wore a First Order military uniform, which included a tunic, pants, a belt, boots, and a cap. They wore a pair of officer rank cylinders on the left side of their tunic's chest.
Goneril made their first appearance, though without a name, in the 2017 film Star Wars: Episode VIII The Last Jedi from the sequel trilogy. Amira Ghazalla played the character, who was credited as "Canady's First Order Commander." Goneril received their name in Jason Fry's adult novelization of the film, which was released on March 6, 2018. In the novelization, Goneril "disdainfully" watches the Black One approach the Fulminatrix's bridge while uttering their first line, "He'll never penetrate our armor," whereas in the film, they speak the line while following Moden Canady away from the bridge's viewport.
The novelization also incorrectly attributes a line spoken by a different bridge crew member of the Fulminatrix in the film to Goneril, as does the non-canon adaptation William Shakespeare's Jedi the Last: Star Wars Part the Eighth by Ian Doescher, published on July 10, 2018. Furthermore, the latter book has Goneril—identified only as "OFFICER 2"—deliver a line—"Resistance bombers make approach, my captain"— that is a modified version of a line spoken by Suday Bascus in the film.