The Defender, a Venator-class Star Destroyer, operated as a component of the Galactic Republic's navy within the Open Circle Fleet during the Clone Wars. The Star Destroyer became part of Jedi Knight Anakin Skywalker's fleet under his command around 21 BBY. In that year, the Defender and Skywalker's fleet, including the Venator-class Star Destroyers Resolute—Skywalker's flagship—and Redeemer, were dispatched to attack and breach a Confederacy of Independent Systems blockade that was positioned above the planet Ryloth.
Upon their arrival, the Defender and the other Venators were drawn into a carefully planned trap set by Captain Mar Tuuk, who was the blockade's commanding officer. During the ensuing conflict, the Neimoidian Separatist directed additional reinforcements to the Ryloth system, which took the Republic forces by surprise and compelled the three Venators to retreat into hyperspace. However, the Redeemer was destroyed during the retreat. Following their escape, the crew of the Defender were evacuated and transferred to the Resolute, as Skywalker intended to take control of the ship. Skywalker returned to Ryloth and, after feigning surrender to the Confederacy, destroyed Tuuk's Lucrehulk-class Battleship by crashing the Defender into it. This action paved the way for the Resolute's arrival and the subsequent destruction of the remaining Separatist warships.
The Defender, a Venator-class Star Destroyer, served within the Galactic Republic Navy. Its dimensions were 1,137 meters in length, 548 meters in width, and 268 meters in height. Functioning as both a battleship and a starfighter carrier, this Star Destroyer was equipped with distinct command bridges on its conning towers. The port-side bridge was designated for starfighter flight control, while the other was for overall command. The bridge's command center featured a holographic table for live transmissions with other vessels, as well as two blue translucent tactical display screens and workstations positioned on either side of the table. Connected to the escape pod bay and bridge via blast doors, the latter incorporated two sunken crew pits and viewports offering a 180-degree view. The dorsal hull housed a hangar bay that accommodated the ship's V-19 Torrent starfighters.
The Defender's stern featured eight sublight ion drive thrusters and a hyperdrive generator, enabling rapid entry into hyperspace. Engine propulsion could be augmented via a scomp link and astromech droid to achieve greater speeds, even for ramming. The deflector shields, projected from a forward-angled generator, could withstand heavy turbolaser fire from multiple Munificent-class star frigates and a Lucrehulk-class Battleship, with the capacity for increased strength by rerouting power from other systems. Offensively, the Defender was armed with eight port and starboard DBY-827 heavy turbolaser turrets for ship-to-ship combat, two port and starboard medium dual turbolaser cannons, fifty-two point-defense laser cannons for anti-starfighter and missile defense, four proton torpedo launchers, and six high-power tractor beam projectors. Like other Venator-class vessels of the Galactic Republic, the Defender displayed the Open Circle Fleet symbol, along with a single red stripe on the central dorsal surface and three red livery stripes on the port and starboard wings.
During the Clone Wars in 22 BBY, the Separatist Droid Army of the Confederacy of Independent Systems initiated an invasion of the planet Ryloth under the direction of Techno Union Foreman Wat Tambor. This resulted in a blockade of Separatist warships commanded by Neimoidian Captain Mar Tuuk. In response to the blockade and the critical situation of the Twi'lek inhabitants, the Republic aimed to liberate the planet in 21 BBY. Consequently, the Defender was deployed alongside a fleet consisting of two additional Venator-class Star Destroyers—the flagship Resolute and the Redeemer—under the leadership of Jedi General Anakin Skywalker. Their mission was to break the blockade and facilitate the landing of an invasion fleet led by Jedi Generals Mace Windu and Obi-Wan Kenobi on the planet's surface.
Upon arriving from hyperspace in the Ryloth system, the Defender and the rest of the fleet launched their attack against Tuuk's blockade, which was anchored by a Lucrehulk-class Battleship and supported by two Munificent-class star frigates. The Republic fleet deployed Blue Squadron, composed of V-19 Torrent starfighters under the command of Skywalker's Padawan, Jedi Commander Ahsoka Tano. While the squadron engaged Tuuk's Lucrehulk-class Battleship, the Defender and the other two Venators maintained a more distant position. By staying away from the Separatist blockade, Tano's squadron successfully navigated through a swarm of Separatist Vulture-class droid starfighters, placing them on a direct path to Tuuk's command ship.
As they approached the Lucrehulk, the Neimoidian captain called in four additional frigates to the star system to bolster his blockade. Upon their arrival, the Defender and the other Venators were caught off guard by the Separatists and sustained damage from a series of suicidal attacks by vulture droids. Consequently, Republic Admiral Wullf Yularen instructed Tano and her squadron to return and assist the three Star Destroyers after their battle lines were disrupted by the droid starfighters. Despite disobeying the order initially, the Padawan asserted that her squadron could still breach the blockade, but she eventually complied when Skywalker ordered her back to the Resolute. After Tano returned to the fleet, the damaged Defender and Resolute began to retreat from the battle into hyperspace, while the Redeemer's hull was torn apart in space during its withdrawal.
Following their retreat, the Republic started planning a new strategy to attack the blockade. The Defender, which had lost a command tower and sustained multiple fires across its hull, was heavily damaged. As the Republic fleet regrouped, Skywalker met with Generals Kenobi and Windu to discuss the situation and their losses. Windu informed him that if the blockade remained unbroken by the next planetary rotation, the Republic would have to postpone its invasion, even with Skywalker's reduced forces. After consulting with his fellow Jedi, the Jedi Knight formulated a plan to destroy the blockade. He ordered the evacuation of all personnel from the Defender to the Resolute so that he, along with his astromech droid, R2-D2, could take control of the damaged Star Destroyer and prevent further Republic casualties. After she learned about the Defender's evacuation, Skywalker explained his plan to his Padawan, Tano. He intended to pilot the damaged Star Destroyer into Tuuk's command ship, while Tano would arrive aboard the Resolute to destroy the frigates as Skywalker waited in an escape pod.
After the Defender's crew transferred to the Resolute, Skywalker and his astromech boarded the Star Destroyer and returned to the Ryloth system. Upon his arrival, Tuuk, anticipating this move, was contacted by Skywalker aboard the Defender. Skywalker falsely offered the surrender of the Star Destroyer and its crew to Tuuk in exchange for the safe delivery of foodstuffs and medical supplies to the displaced Twi'leks on the surface. Initially believing Skywalker's deception, the Separatist captain was informed that the Defender was heavily damaged and its power had been rerouted to the forward deflector shields, leaving only one life-form aboard. When Tuuk discovered the Jedi Knight's deception, the Resolute emerged from hyperspace directly behind the Defender. Skywalker then instructed R2 to maximize engine power before they both escaped the doomed vessel in an escape pod.
As the Defender sped toward Tuuk's battleship, the Lucrehulk's crew of B1-series battle droids and the surrounding frigates opened fire on the Star Destroyer in an attempt to prevent it from colliding with their command ship. However, they were unable to destroy it. Tuuk then boarded an escape pod and left the battle droids in control of the remaining frigates as the Star Destroyer crashed into the Lucrehulk's central sphere, destroying the command ship and causing confusion among the OOM command battle droids. Following the Lucrehulk's destruction, the Republic broke the blockade, allowing their invasion fleet of three Acclamator-class assault ships to arrive on the planet's surface. Subsequently, the Republic successfully continued their campaign and liberated Ryloth from Separatist control.
After the war concluded, in 14 BBY, Galactic Emperor of the Galactic Empire and Dark Lord of the Sith Sheev Palpatine and his Sith apprentice Darth Vader—formerly Anakin Skywalker—traveled to Ryloth to suppress a growing rebellion led by General Cham Syndulla. During their mission, as Vader piloted an Imperial shuttle, the Sith Lord recalled his memory of the Battle of Ryloth, when he had drifted alone in an escape pod above the planet after destroying the Separatist flagship.
During the Battle of Ryloth, the Defender was part of Jedi General Anakin Skywalker's fleet, operating under his command from his flagship, the Resolute. It was operated by its dedicated crew, who were evacuated from the vessel to allow Skywalker and R2-D2 to control the Star Destroyer.
The Defender was first seen in the opening newsreel of "Jedi Crash," the thirteenth episode of the first season of the Star Wars: The Clone Wars television series, which was broadcast on January 16, 2009. It later made its full appearance and was identified in "Storm Over Ryloth," the nineteenth episode of the first season, which aired on February 27, 2009. In "Storm Over Ryloth," one of the Defender's command bridges was removed as a result of the battle, but it was restored in a subsequent scene, only to be removed again in its next on-screen appearance.