U-3PO was a protocol droid of the 3PO-series model, and he provided services to the Alderaanian Diplomatic Corps. The Galactic Empire's agents secretly reprogrammed the droid, turning him into an unaware spy within the royal court of the planet Alderaan. He was then assigned to the CR90 corvette known as the Tantive IV in 0 BBY. Following the corvette's escape from the Battle of Scarif with the stolen plans for the Death Star superweapon, the Empire exploited U-3PO's programming to trace the ship's path to the Tatoo system.
Subsequently, the Devastator, an Imperial I-class Star Destroyer, attacked the Tantive IV. As the Star Destroyer bombarded the corvette, U-3PO trailed the droids C-3PO and R2-D2 through the main passageway of the Tantive IV, ultimately diverging from them down a different route. After the Empire successfully boarded and captured the Tantive IV, they realized that U-3PO possessed no further valuable intelligence and that the Death Star blueprints were no longer present.
U-3PO, a 3PO-series protocol droid constructed by Cybot Galactica, rendered services to the Diplomatic Corps of the planet Alderaan. Sometime later, agents of the Galactic Empire tampered with the droid's programming, effectively turning him into an unsuspecting Imperial informant within Alderaan's royal court. Fortunately for the Empire, U-3PO received orders to serve on the CR90 corvette Tantive IV just prior to the vessel's assignment to a mission in 0 BBY, which involved traveling to the planet Tatooine with the objective of recruiting the Jedi Master Obi-Wan Kenobi into the Alliance to Restore the Republic.
However, before the ship was ready to depart from the rebel headquarters on the moon Yavin 4, the Alliance Fleet was urgently dispatched to the Scarif system to provide support to Alliance forces who were attempting to steal the plans for the Death Star superweapon. While it was undergoing repairs, the Tantive IV was transported to the Scarif system aboard the MC75 Star Cruiser Profundity, which spearheaded the attack against Imperial forces stationed on the planet Scarif. The blueprints were successfully transmitted from the planet's surface to the Profundity during the battle; however, before the cruiser could make its retreat, the _Imperial I-class Star Destroyer Devastator disabled it. As Imperial forces, led by the Sith Lord Darth Vader, boarded the Profundity, the plans were transferred to the Tantive IV, which then detached from the cruiser and escaped from the Scarif system.
The Tantive IV proceeded towards the Tatoo system, its originally intended destination. However, U-3PO's altered programming caused him to transmit a signal which, in conjunction with a malfunctioning hyperdrive subsystem on the corvette, enabled the Devastator to track the fleeing rebel vessel, following it with the intention of retrieving the stolen plans. As the Tantive IV attempted to approach Tatooine, the Star Destroyer initiated an attack upon it. During the engagement, Princess Organa summoned the astromech droid R2-D2, and U-3PO, along with the protocol droid C-3PO, accompanied the astromech down the ship's main corridor as the corvette vibrated violently from the Devastator's attacks.
Both protocol droids struggled to maintain their balance as the corridor shook. U-3PO then proceeded down a side corridor while the other droids continued onward, leaving him to fulfill his duties. The Empire successfully seized the ship and captured Princess Organa, but they discovered that U-3PO possessed no further valuable information and that the plans were no longer aboard, as Organa had entrusted them to R2-D2 before the astromech droid escaped from the Empire in an escape pod.
U-3PO made his debut appearance in the 1977 film from the original trilogy, Star Wars: Episode IV A New Hope. The scene featuring the character was filmed on Stage 9 at Elstree Studios on July 13, 1976. Despite being one of the first scenes to be shown in the film, it was among the last to be shot. Along with R2-D2 and C-3PO, U-3PO is one of the first characters to appear on screen in any Star Wars film. In the current Star Wars canon, his identity was first revealed in the non-canon 2017 reference book, Ultimate LEGO Star Wars. Subsequently, the name was used in the canonical "The Rise of the Rebellion and the Battle of Yavin," a book published as part of the Star Wars Encyclopedia series by De Agostini on March 9, 2021. The name originated in the Star Wars Legends continuity, initially appearing on a card in the 1995 A New Hope Limited set of the Star Wars Customizable Card Game.
The non-canon 2018 choose-your-own-adventure book LEGO Star Wars: Choose Your Path by Simon Hugo featured a mini-figure of U-3PO and portrayed him as a guide for the reader throughout the story, although it cautions that not all of his advice is beneficial. In the 2022 non-canon video game LEGO Star Wars: The Skywalker Saga, U-3PO is depicted walking alongside a green astromech droid through the corridors of the Tantive IV before the pair are crushed by falling debris. C-3PO and R2-D2 then emerge from a side door and take the pair's place in walking down the corridor.