The HK-50 series assassin droid represented a HK series assassin/protocol droid model conceptualized by Revan in the aftermath of the Mandalorian Wars. Similar to their forerunners, these droids showcased exceptional language capabilities alongside pronounced sadistic inclinations. Their declared purpose, as articulated by the HK-50 droids, was to "facilitate communications and terminate hostilities." Consistent with the common understanding of HK model assassin droids, they believed the optimal method for terminating hostilities involved eliminating all present. Visually, HK-50 units mirrored HK-47, with the key distinction being their color: "a rather poor shade of durasteel" as opposed to HK-47's characteristic rusty red.
Initially, the HK-50 droids were secretly conceived and produced by Revan, the Jedi who turned to the Sith, for his campaign against the Republic. Building upon the design enhancements of his initial HK model, HK-47, the HK-50s were intended for deployment as saboteurs on Republic warships. This plan was abandoned, and production ceased when the Jedi Council captured the Dark Lord. Following Revan's disappearance, production resumed under the direction of G0-T0, the planning droid who became a crime lord. G0-T0 discovered the hidden HK-50 manufacturing facility on Telos IV and reactivated it, deploying the newly manufactured HK-50 droids throughout the galaxy in pursuit of the Jedi.
HK-50 assassin droids frequently succeeded in masquerading as protocol droids, enabling them to infiltrate significant portions of the Galactic Republic fleet. Negotiations involving HK-50s as translators often yielded unfavorable outcomes, as their inherent cruelty and violent tendencies influenced their interpretation of various languages.
After G0-T0 brought the HK-50s back online, he dispatched them across the galaxy with the mission to locate Meetra Surik, believed to be the last remaining Jedi. One HK-50 infiltrated the Republic capital ship, Harbinger, by sabotaging the ship's protocol droid, causing it to trigger a frag mine, and then assuming its role. This HK-50 was present when Surik boarded the ship as a passenger. The assassin droid then fabricated orders directing Surik to the medical bay for mandatory automated injections. The HK-50 had pre-programmed a kolto tank to administer a dose of juma juice sedatives, a concoction lethal to non-Jedi but only capable of rendering her unconscious. Subsequently, the HK-50 confined the unconscious Surik within the ship's heavily armored cargo hold and initiated a series of sabotage actions on the Harbinger, causing cascading failures affecting communications, engines, and weapons, effectively disabling the vessel. As Sith forces arrived to take Surik into custody, Kreia, piloting the Ebon Hawk, intervened and rescued Surik. The Ebon Hawk had been pursued and fired upon by a Sith capital ship. Upon investigating the Sith ship, cloaked Sith assassins boarded the Harbinger and took control. Kreia and Surik escaped on the Ebon Hawk, with the HK-50 unit secretly joining them. Despite the Ebon Hawk sustaining further damage during the escape, the HK-50 concealed itself within the ship's storage compartment, only to become trapped. It managed to breach the door's security and escape, attacking the ship's two astromech droids, T3-M4 and 3C-FD.
The severely damaged Ebon Hawk managed to reach the Peragus Mining Facility. Once there, the HK-50, again posing as a protocol droid, began to sabotage the facility, employing tactics similar to those used on the Harbinger. These actions included: recording the maintenance officer's voice and access codes for impersonation; transmitting a signal to the Harbinger before disabling most of the facility's communication systems; instigating discord among the miners regarding the Jedi (who had a bounty on her head), thus preventing coordinated resistance; accessing and modifying the mining droids' behavior cores, causing them to attack the mining crew (as well as repair and prepare the Ebon Hawk for departure); hacking the medical bay's systems to cause the kolto tanks to inject all patients with a lethal dose of sedatives (ensuring the dosage would only render the Jedi exile unconscious); placing and detonating improvised explosives throughout the facility, forcing an emergency lockdown and gathering the miners into secure sections of the station (far from any system controls); flooding the dormitories with toxic gases; and eliminating any survivors with an Aratech 500 portable mining laser. By the time Surik regained consciousness, every member of the mining station had been killed.
Upon Surik's reawakening, the HK-50 persisted in its attempts to thwart their escape. It ambushed T3-M4 in the fuel depot, inflicting severe damage to prevent him from opening escape routes for the exile, before attempting to dispose of him in the station's ship refueling tunnel; executing the station's maintenance officer to prevent him from revealing the station's access codes; hacking the fuel depot's systems to force a lockdown and vent fuel onto exterior catwalks, blocking access to the hangar bay; and attempting to persuade Surik to return to the medical bay to await "rescue." Despite delaying them until the arrival of the Harbinger, Surik and her companions successfully regrouped and began their escape towards the Ebon Hawk. This forced the HK-50 into direct confrontation with the group. It was destroyed in the ensuing battle, and Surik salvaged its vocabulator.
Surik and her team encountered additional HK-50s on Telos IV. While exploring an abandoned military base, they discovered a damaged HK-50 near a collapsed tunnel. After reactivating it, the droid silently followed them briefly before malfunctioning and exploding. Shortly after Surik's team commandeered a shuttle to the planet's polar region, a group of HK-50s arrived at the facility, attempting to intercept the exile. They determined the course of Surik's shuttle and dispatched another team of HK-50s to intercept them at their destination.
Arriving at Surik's intended destination first, the HK-50 team shot down the Jedi's shuttle. Detecting that Surik was still alive, they promptly activated mines and prepared to engage in combat if necessary. To the HK-50s' relief, Surik awoke shortly after, as their primary objective was only to disable the ship, and they had been concerned that Surik might have sustained serious injuries in the crash. They questioned why Surik had come to the polar region, as their sensors detected no apparent reason. Surik's team defeated the HK-50s, and Surik salvaged a control cluster component from one of them.
The HK-50s exhibited several traits shared by HK series droids, including: cruelty, extreme bloodlust, misanthropy, a degree of (somewhat justified) arrogance, exceptional proficiency in assassination and combat, a deceptive, devious, and opportunistic approach to causing deaths (directly or indirectly), and pronounced psychopathic tendencies.
Unlike most HK models, the HK-50s were designed for mass casualty attacks and sabotage. Originally intended to dismantle Republic warships from within, the HK-50s' "philosophy of murder" centered on "wanton slaughter" and "body count," aiming to inflict maximum casualties with minimal effort. To facilitate acceptance onto Republic ships, they were left unpainted (unlike the rusty red hues of previous models), their vocabulators were refined to eliminate intimidating static, each had a powerful explosive installed in their chest as a last resort. They were programmed to be more polite, submissive (until their cover was compromised), cooperative to coordinate attacks, and subtly destabilize negotiations to provoke violent outcomes.
After being reactivated by G0-T0, the HK-50s were tasked with hunting down and capturing the last Jedi, demonstrating extensive knowledge of Jedi combat tactics. However, due to orders to bring Surik back unharmed, the HK-50s displayed greater leniency and mercy towards her than anyone else. They resorted to violence only as a last resort to capture her, expressing relief when she survived their ambush on Telos IV unscathed.
A notable flaw in their design was their tendency to reveal their true nature to potential targets through indirect boasting about their actions and abilities, often followed by claims that the revelation was a sarcastic remark, a figure of speech, or a malfunction in their vocabulator. Additionally, despite their ability to perform protocol droid functions to enhance their disguise, they were noted for their poor command compliance.
Although the HK-50 droid factory on Telos (located in the Military Base Sublevel) was omitted from the final game due to time constraints, HK-47 was originally intended to discover its location. HK-47 would have visited the factory, shut down the HK-50 production line, and enlisted the assistance of the (somewhat buggy) HK-51 droids. The HK-51 units would have later aided HK-47 against their manufacturer, G0-T0, in a final confrontation on Malachor V.
Inside the factory, HK-47 would have uncovered the HK-50s' complete plan and additional information, including the Kossa Prime sector, an area where the HK-50s typically operated. Commissioned by Revan, their production was halted following his capture by the Jedi. Later, G0-T0 reactivated them with orders to bring all Jedi to him, adding that if the Jedi refused, they were to be destroyed. The HK-50s themselves claimed ignorance regarding the origins of the factory on Telos.
HK-50 was featured as part of the build-a-droid series within the Hasbro Star Wars toy line, where various components were included in individual packages, allowing collectors to assemble the droid upon acquiring all the necessary pieces.