The Guardian was a Star Dreadnought of the Executor-class. Initially, Admiral Gaen Drommel of the Galactic Empire held command of it, positioning it near Coruscant when the Battle of Endor's outcome became known. Drommel then piloted the Guardian to the vicinity of his homeworld, Oplovis, where he established himself as a warlord. Following repeated assaults on New Republic territories, Drommel's fortunes shifted, and the Guardian received significant damage during the Battle of Tantive V in 4 ABY. Drommel escaped into hyperspace, but the vessel's damaged hyperdrive caused the Guardian to materialize in the Fardon system instead of its intended destination. With its hyperdrive disabled, it entered orbit around the planet Soullex, remaining there for over a decade while Drommel attempted repairs.
Around 16 ABY, the New Republic discovered that the Guardian was acquiring parts through its Lambda-class shuttles. Cryle Cavv and Sienn Sconn, two ship thieves, were tasked with tracing the shuttles to their source and seizing the Guardian. After liberating several New Republic prisoners, Cavv and Sconn successfully reprogrammed the nearly repaired hyperdrive to jump directly into a New Republic fleet during Drommel's test. Drommel refused to surrender, but Colonel Niovi, one of his officers, killed him and surrendered the vessel to the New Republic, assuming command.
The New Republic reassigned the Guardian to the Third Fleet, under the leadership of Admiral Gial Ackbar. Ackbar utilized the Guardian as his flagship, leading New Republic fleets in a series of engagements against the Empire. These included the Second Battle of Champala and the Battle of Anx Minor, which forced the Empire, then under Gilad Pellaeon, to retreat to a small number of sectors. During the Yuuzhan Vong War, the Guardian provided protection for Chief of State Cal Omas before being assigned to Traest Kre'fey's Fleet Group One at Kashyyyk. Following the establishment of a new government, the Galactic Alliance, the Guardian was redeployed to Mon Calamari to safeguard the Alliance headquarters. It subsequently participated in the Battle of Mon Calamari against the Yuuzhan Vong.
The Guardian was one of the Executor-class Star Dreadnoughts, measuring 19 kilometers in length. While it typically housed over 280,000 personnel, this number decreased to 250,000 during its decade-long stay above Soullex, which included nearly 40,000 soldiers. The ship was outfitted with several prefabricated garrison bases, which its commander, Gaen Drommel, employed to control the Fardon system after the Guardian's escape from New Republic forces at the Battle of Tantive V. Its standard armament included 250 turbolaser emplacements, 250 heavy turbolaser emplacements, 250 concussion missile emplacements, and 40 tractor beam installations. However, after Tantive V, these numbers were significantly reduced, with over half of some emplacements being rendered unusable. The hyperdrives, normally rated at class 2.0 with a class 10 backup, were also rendered inoperable until Drommel's forces repaired them. The ship also carried a complement of _Lambda-class T-4a shuttles, which Drommel utilized during the Guardian's period of inactivity as the primary means of transportation for gathering materials to repair the vessel.
The Guardian featured a spacious command deck, located near the admiral's quarters. It included a large admiral's lounge, which was elegantly furnished and adorned with flowers under New Republic ownership. The ship also contained a detention block for holding prisoners; under Drommel's command, many of these were New Republic personnel who had inadvertently entered the Guardian's vicinity. Interrogation rooms were available for questioning these individuals. The ship's engineering room provided access to the hyperdrive, allowing coordinates to be entered directly, bypassing the navigation computer.
Upon its completion, the Guardian was given to Admiral Gaen Drommel of the Galactic Empire as a reward for his destruction of Rebel bases on Aargonar 3, Randa, and the Valsedian asteroid belt. At the time of the Battle of Endor, the Guardian was stationed close to Coruscant. The battle resulted in the death of Emperor Palpatine and the defeat of the Imperial fleet at Endor. Upon learning of this, Drommel used the Guardian to flee Coruscant, heading to the space surrounding his homeworld of Oplovis, with the intention of using his fleet to establish his own personal empire. Shortly after Endor, the Guardian, under Drommel's command, along with three Imperial-class Star Destroyers, initiated a campaign of terror against the New Republic's safe worlds and bases, significantly impacting the fledgling government.

However, Drommel's campaign was short-lived. The New Republic had been studying the weaknesses of Imperial Star Destroyers, and they used this knowledge to great effect when they engaged Drommel's fleet at the Battle of Tantive V in 4 ABY. Two of Drommel's Star Destroyers were destroyed, the third was captured, and the Guardian was heavily damaged and forced to retreat after the Republic targeted its weapon and shield systems and crippled its hyperdrive. The Super Star Destroyer managed to jump to hyperspace, but it arrived in the Fardon system of the Outer Rim instead of its intended destination. With its hyperdrive disabled, the crippled vessel positioned itself above the planet Soullex, where it struggled to maintain orbit. Drommel subjugated the system, deploying three prefabricated garrison bases to the planet below.
Drommel began repairing the Guardian, sending Lambda-class shuttles to Imperial-controlled worlds for assistance. He planned to complete the repairs as quickly as possible, but the fall of the Empire's remnants to the New Republic meant that Imperial worlds could not spare any aid. Drommel intended to use the Guardian as the centerpiece of a campaign to destroy the New Republic, so he kept his search for parts and assistance as discreet as possible. Around 7 ABY, Drommel began receiving the necessary parts to repair the vessel's hyperdrive, but the ship remained in place for over a decade. During this time, several New Republic personnel unknowingly hyperjumped into the Fardon system and were detained by the Guardian. New Republic Intelligence operative Shandria L'hnnar led an assault team to locate the vessel, but they were also captured.
Eventually, New Republic probe droids began encountering Drommel's Lambda shuttles as they retrieved parts. Further investigation revealed that these vessels were part of the Guardian's complement. In 16 ABY, Cryle Cavv, a ship thief working for the New Republic, learned from his contacts about a meeting on the planet Vohai between black marketeer Burgo Teage and an Imperial Lambda shuttle regarding the sale of hyperdrive parts. General Airen Cracken of New Republic Intelligence realized that capturing the Guardian would be a major victory for the Republic, and he and Cavv recruited Cavv's nephew Sienn Sconn, another ship thief. Cavv and Sconn disrupted the meeting on Vohai, seized the shuttle, and followed its navigation computer back to its origin point at Soullex.
While docking with the Guardian, Cavv and Sconn disabled the shuttle's comm unit to avoid speaking to the vessel's comm operators and revealing their deception. Upon docking, they ambushed a pair of stormtroopers and donned their armor as a disguise. They also captured a protocol droid, CT-EX, and reprogrammed it to their purposes. Drommel, alerted to the ship's communications problem and suspicious, ordered the shuttle to be examined. When the search team found the stunned stormtroopers, Drommel issued an alert for the impostors. He ordered the hyperdrive repairs to be accelerated, planning to leave the system and return to Imperial space within the next 36 hours.

However, Cavv and Sconn were already heading to Detention Block 220, where the New Republic prisoners were being held. All but one guard had been sent out to find the intruders, and the remaining guard was quickly disabled. The thieves freed the prisoners, including Shandria L'hnnar, and recruited them into their plan. Cavv and Sconn headed for the engineering room, intending to manually set the hyperdrive to jump into New Republic-friendly space, and signaled CT-EX as their fallback plan. They arrived as Drommel was receiving the go-ahead to jump within the next ten minutes. However, their tampering triggered an alarm, and Drommel returned with a group of soldiers to take them into custody. His interrogation proved fruitless; however, CT-EX was reprogramming the hyperdrive's coordinates at the same time. Drommel sent the thieves back to the detention cells to await the hyperdrive test, but they were intercepted by L'hnnar and the other prisoners.
Drommel ordered the ship to jump. The Guardian successfully jumped into the middle of a New Republic fleet led by the cruiser Equity. Equity's captain, Volahn, ordered the Guardian to surrender. Drommel refused, and the entire New Republic infiltration party—Cavv, Sconn, and the prisoners—forced their way onto the command deck, drawing their weapons on the deck staff, who in turn drew on them. Cavv addressed the crew, telling them that peacefully surrendering the vessel would help their case with the New Republic. Drommel had had enough and ordered the crew to open fire, but Sconn persuaded them to stand down and lower their weapons. Enraged, Drommel drew a blaster on Cavv, but his subordinate, Colonel Gastos Niovi, stopped him, strangling him to death. As acting commander, Niovi surrendered the Guardian to the New Republic.
With the Guardian in its possession, the New Republic began refitting the vessel. A year after its capture, the New Republic added the ship to its Third Fleet. Admiral Gial Ackbar took command of the vessel, and under his leadership, the Third and Fifth Fleets engaged Imperial Admiral Gilad Pellaeon in several major battles, most notably the Second Battle of Champala and the Battle of Anx Minor. At Anx Minor, Ackbar achieved victory at the last minute by concentrating fire on the engines of the experimental EX-F, which exploded and destroyed the surrounding Imperial Star Destroyers. Under Ackbar, the Guardian, and the fleets' combined assault, Pellaeon was forced to retreat, losing significant territory and ultimately leading the Empire to seek peace.
The Guardian remained in New Republic custody throughout the Yuuzhan Vong War. In the weeks leading up to the Battle of Ebaq 9 in 28 ABY, a major victory against the invading Yuuzhan Vong, New Republic Chief of State Cal Omas isolated himself aboard the Guardian, which remained safely cruising between the stars for the duration of the battle. Following the Republic's victory, the Guardian joined Admiral Traest Kre'fey's Fleet Group One at Kashyyyk. There, Omas and Jedi Master Luke Skywalker met in the vessel's admiral's lounge to discuss the formation of a new government, the Galactic Federation of Free Alliances.
When the Galactic Alliance established itself on the planet Mon Calamari, the Guardian was recalled to join the planet's home fleet. In 29 ABY, word arrived of a large-scale Yuuzhan Vong assault being planned on Mon Calamari. The Alliance used this as an opportunity to deploy half its fleets to retake Coruscant, which had fallen two years prior, while the other half defended Mon Calamari. The Guardian was among the latter, taking up station at Mon Calamari Extreme, a position in the outer reaches of the Calamari system. When the Yuuzhan Vong vessels arrived and launched their waves of starfighters, the Alliance countered with its own starfighter attack to clear firing lanes between the enemy capital ships and their own. As lanes opened, the starfighters evacuated those areas, and the Guardian and the companion vessel Harbinger moved forward to fire salvos into the heart of the Yuuzhan Vong fleet. As they moved further into the system, the Yuuzhan Vong diverted their dovin basal shielding towards the front of the fleet's advance. The Alliance sent Star Destroyers in to flank them, forcing them to relocate the shields and allowing Guardian, Harbinger, and the Mon Calamari Star Defender Viscount to continue their barrage from the front. Alliance bombers then attacked the Yuuzhan Vong fleet, and the enemy vessels shifted their dovin basals to protect themselves, freeing Guardian to eliminate waves of yorik-et starfighters instead. The Yuuzhan Vong soon pulled a flotilla away from their fleet to reinforce against the concurrent Galactic Alliance attacks elsewhere, but even with the two opposing armadas on more equal footing, the Alliance continued to fall back toward Mon Calamari. On the verge of retreat, the Alliance was saved by the arrival of the planet Zonama Sekot in the Coruscant system, which convinced Yuuzhan Vong Warmaster Nas Choka to call off the attack on Mon Calamari and redirect his resources to Coruscant.

Gaen Drommel, a charismatic commander of the Guardian, inspired loyalty in his men. He was both feared and respected. Having learned the value of fear as a motivator from Wilhuff Tarkin, Drommel was severe with those who disobeyed or displeased him, often executing them immediately. He disliked those who were not thorough or made assumptions, and his men ensured they had all the information before speaking to him. Drommel's strict methods earned him great obedience; his soldiers always double-checked their work when he was watching, and they worked extra hard without breaks to complete tasks quickly when required. The admiral was attentive to events aboard his ship, personally overseeing important repairs and aware of the actions of intruders and saboteurs.
As the commander of his ship, Drommel aspired to be a warlord, intending to use the Guardian to carve out his own territory from the remnants of the Empire and later as the centerpiece of an attempt to destroy the New Republic. However, his refusal to surrender and his willingness to fight to the end resulted in his death at the hands of Colonel Niovi, who killed him for refusing to surrender to the New Republic forces holding him and the ship's command deck crew at gunpoint. Upon Drommel's death, Niovi assumed acting command of the Guardian, surrendering it to New Republic forces.
Under the command of Gial Ackbar, who had led the fleets of the Rebel Alliance and its successor, the New Republic, for much of the Galactic Civil War, the Guardian achieved significant victories for the New Republic. A skilled strategist, Ackbar oversaw the Guardian's campaign against Gilad Pellaeon of the Imperial Remnant. Alongside the Third and Fifth Fleets, the Guardian under Ackbar fought at Champala, defeated the experimental EX-F at Anx Minor, and forced Pellaeon to retreat and the Remnant back to eight sectors in the Outer Rim, ultimately leading the Empire to sue for peace.
The Guardian initially appeared as a sidebar in Louis J. Prosperi's roleplaying game sourcebook Wanted by Cracken, as part of Gaen Drommel's character profile. As the book is set in 7 ABY, its information on the Guardian ends with the vessel in orbit over Soullex. The sourcebook provides several scenarios for players to find the Guardian, including tracking a Lambda-class shuttle back to Soullex, replacing its crew and boarding the Guardian, discovering the Super Star Destroyer while scouting the Fardon system, and making an emergency jump from a battle that ends up at Soullex. Two for One, a short story by Paul Danner from Star Wars Adventure Journal 15, later used several of these ideas in telling the story of how the New Republic captured the Guardian. From then on, the Guardian made several appearances in novels and Essential Guides under New Republic custody.
In Wanted by Cracken, Guardian is listed as an 8,000-meter Super-class Star Destroyer. Since then, that class has been retconned in sources such as the Databank's Super Star Destroyer entry and Starship Battles, to be the 19,000-meter Executor-class Star Dreadnought. However, the original image of the Guardian in Wanted by Cracken shows it much closer to the 19-kilometer length—approximately eleven to twelve times longer than the Imperial Star Destroyers in the picture—than the 8-kilometer size listed in the statistics. The Star Wars Blog article, The Imperial Warlords: Despoilers of an Empire, definitively stated the Guardian to be 19,000 meters long.