K-3PX was a black 3PX-series protocol droid that belonged to the Sith Lord Darth Vader during the height of the Galactic Civil War, stationed at the Imperial citadel on Gamandar. K-3PX played a vital role in Admiral Griggor Tower's capture of Rebel agents Lando Calrissian and Chewbacca/Legends in 3 ABY—later, he would inform Vader of Tower's endangerment of Vader's coveted target Luke Skywalker on Iskalon, leading to Tower's execution.
A black-colored 3PX-series protocol droid, K-3PX served the Galactic Empire during the height of the Galactic Civil War, the personal property of the Sith Lord Darth Vader. Vader put K-3PX to work under the command of Admiral Griggor Tower at the citadel on Gamandar, in the subjugated Iskalon system. In 3 ABY, several Rebel agents traveled to nearby Iskalon searching for any trace of disappeared Rebel soldier Tay Vanis, who had been last seen investigating secret Imperial plans in the system. On Iskalon, they received false information from an Iskalonian named Kendle—an Imperial informant—that Vanis entrusted all his information on the Empire's plans to K-3PX, which he identified as Vanis' personal droid. Kendle pointed them to Gamandar, where several of their number—Lando Calrissian and Chewbacca, accompanied by native Iskalonian Mone and the droids C-3PO and R2-D2—traveled in search of K-3PX and Vanis.
Posing as an Imperial-friendly smuggler named "Drebble," Calrissian seemingly purchased K-3PX from Admiral Tower, and not only revealed himself and his friends as Rebel agents to K-3PX, but also told the droid that Luke Skywalker—the Rebel hero of the Battle of Yavin and a highly desired target of Vader—was part of the complement on Iskalon. However, Calrissian and his group had no idea how thoroughly they had been outmaneuvered. Not only was K-3PX loyal to the Empire, but Kendle's subterfuge had given Tower advance knowledge on Calrissian's arrival, resulting in the Rebels' imprisonment. Tower went one further, attacking Iskalon directly and causing the "Iskalon effect," a massive tidal wave that devastated the water-covered world. After learning of Skywalker's presence on Iskalon, K-3PX then reported directly to Vader himself, informing the Sith Lord that Tower had "overstepped" himself by attacking the planet and risking the Rebel's life, knowing that Vader wanted Skywalker alive. Outraged, Vader directed K-3PX to arrest Tower, and shortly afterward had the Admiral executed.
A 3PX-series protocol droid with a distinct black plating, K-3PX was loyal to the Empire and operated efficiently and ruthlessly in the service of its employer. K-3PX was quick to turn on Griggor Tower the moment the tides turned against the Admiral, facilitating his arrest and death at the hands of Darth Vader.
K-3PX first appeared in Star Wars (1977) 75, written by Mary Jo Duffy, illustrated by Ron Frenz and released in 1983. In 2008, K-3PX received its first action figure, appearing alongside Darth Vader in the Star Wars: The Legacy Collection line, in doing so creating an inconsistency with its name. The Marvel comic issues featuring K-3PX consistently spell the droid's name "K3PX." The Hasbro Legacy Collection, however, spelled the designation as "K-3PX," using the hyphen customary of many droids in the Star Wars universe, which was later confirmed by The Complete Star Wars Encyclopedia.