The Merciless served as the flagship for both Tyber Zann and the Zann Consortium, and was his personal Aggressor-class destroyer. Its design, the foundation of the Aggressor-class destroyer, was discovered by the Zann Consortium amidst the wreckage of the destroyed first Death Star. Recognizing its potential, it was seized from Imperial control and delivered to Tyber Zann. Zann first deployed the Merciless with devastating results above Carida, leading to the further production of Aggressor-class destroyers. Following the Empire's defeat above Endor, Zann, accompanied by a fleet, advanced on Kuat, where they encountered the Rebel fleet attacking the surviving Imperial warships. Alongside the Rebels, the Merciless engaged the faltering Imperial forces until the Eclipse was seized.
This Aggressor-class destroyer, the Merciless, was a modified vessel that had been purloined from Imperial dockyards. Its hull was painted black, accented by white trim, and adorned with menacing murals depicting a krayt dragon stretching along each side. At the ship's front, it boasted two enormous, linked ion and plasma cannons. The Merciless also featured a turbolaser battery positioned on each side of its rear fins. A shield generator, reminiscent of those found on the Imperial Star Destroyer, was located atop the bridge. To enhance stealth capabilities, Tyber Zann had a cloaking device installed.
The Empire originally created the Merciless as the prototype Aggressor-class destroyer, making it the first of its kind. After the Zann Consortium discovered its schematics within the ruins of the first Death Star, it was stolen. Subsequently, the ship underwent modifications and received a unique paint scheme. The Merciless was finished in 3 ABY. The first sighting of Tyber Zann using the ship occurred over Carida. There, he was met by Admiral Thrawn, who informed him of the death of Prince Xizor, who was planning to purchase a Sith artifact. Thrawn then betrayed Zann above Carida. Using a HVs-2 hypervelocity gun situated on the planet's surface, Thrawn destroyed an Interceptor IV frigate that belonged to Zann. Zann retaliated by deploying his fleet, including the Merciless. Their battle continued until Tyber's associate Bossk managed to steal the artifact. Bossk escaped aboard the Hound's Tooth and delivered the artifact to Thrawn on his flagship, the Admonitor. Thrawn immediately departed, leaving the rest of his fleet behind with orders to eliminate Tyber Zann's forces. However, the Zann Consortium swiftly defeated the Imperial ships, leading Zann to realize the effectiveness of the Aggressor-class Destroyer.
Following the destruction of the second Death Star, the Merciless, along with an accompanying fleet, attacked the Imperial forces stationed above Kuat. Their objective was to seize the incomplete Eclipse. Simultaneously, the Rebel fleet arrived, aiming to destroy all Imperial vessels. The two factions formed a tentative alliance and commenced an assault on three Cardan V-class space stations. Meanwhile, a boarding shuttle approached the Eclipse, allowing a team to board and take control of the massive warship. The Zann Consortium gained the advantage and annihilated both the Rebel and Imperial forces.