A-3DO, often referred to as ThreeDee, functioned as a 3DO protocol/service droid from Duwani Mechanical Products, with expertise in starship upkeep and a wide array of household tasks. After Jedi trainee Andur Sunrider purchased him, ThreeDee became a companion to Sunrider, his wife Nomi, and their daughter Vima, providing assistance and maintaining Andur's vessel, the Lightside Explorer. Throughout his time with the Sunriders, the droid encountered various incidents, including being taken captive—an event that resulted in the death of his owner, Andur—and suffering the loss of an arm due to an attack by mercenaries working for Bogga the Hutt. Following Andur's demise, ThreeDee went with Nomi to the planet Ambria, where she underwent training in the Force under the guidance of Jedi Master Thon and successfully defended against multiple assaults by the Hutt's underlings.
Duwani Mechanical Products built A-3DO, a 3DO protocol/service droid, who was later acquired for 1,500 credits by Andur Sunrider, a Jedi trainee hailing from Darada. The droid accompanied Sunrider and his spouse Nomi aboard Andur's starship, known as the Lightside Explorer, where his main responsibility was ensuring the ship's operational status. A-3DO also engaged in other activities, such as playing music on a mandolin, but he primarily devoted his time to caring for the Sunriders and expressing concern for their well-being when he wasn't maintaining the vessel. The droid regarded the Sunriders as his own family and insisted on being addressed by the more informal name, ThreeDee.
When Andur received an invitation from Jedi Master Chamma—a comrade of Andur's grandfather, Jev Sunrider—to receive instruction in the Force under his tutelage on the planet H'ratth, ThreeDee joined his masters on their journey. While on the planet, Nomi gave birth to a daughter, Vima. Shortly thereafter, Master Chamma determined that he could no longer continue Andur's training in the ways of the Jedi and directed his apprentice to travel to Ambria, located in the Stenness system, where he would complete his education under the Tchuukthai Jedi Master, Thon. Chamma presented Andur with several Adegan crystals—highly valuable for constructing lightsabers—as gifts to bring to his new master. However, before they could depart, A-3DO had to replace an ion exciter to restore the Lightside Explorer's hyperdrive to working order. Once again, A-3DO found himself traveling to another planet alongside the Sunriders.
The Lightside Explorer made its way to the Stenness system, where it made a stop at a hyperspace terminal for servicing and customs inspection. ThreeDee and the Sunriders disembarked from the ship to explore the station, but they were soon ambushed by thugs from Bogga the Hutt's organization, who had overheard Andur mentioning the Adegan crystals to Nomi; the criminals seized the droid as a distraction. When Andur confronted the gang members, one of them hurled a gorm-worm at Andur; the small creature bit Sunrider, resulting in his almost immediate death. Nomi, unexpectedly, picked up her deceased husband's lightsaber, defending Vima and ThreeDee, and drove off the attackers, much to ThreeDee's relief. The trio quickly escaped in the Lightside Explorer and set a course for Ambria.
Upon arriving on Ambria, Nomi decided to venture out on her own with Vima in search of Master Thon, leaving ThreeDee behind to watch over the ship. Sometime later, A-3DO was caught off guard by Bogga the Hutt's mercenaries, who forcefully entered the Lightside Explorer. The Hutt gangster, who desired the Adegan crystals, had decided to bring his sail barge and gang to Ambria in pursuit of Nomi. ThreeDee's arm was destroyed, and the ship was plundered.
Following yet another encounter with Bogga's thugs at Thon's residence, whom she had finally located, Nomi returned to the ship with the Jedi Oss Wilum, another of Thon's students, and retrieved A-3DO. Wilum took on the task of repairing the damage inflicted upon ThreeDee, but his progress was delayed for several months due to a scarcity of parts. Eventually, Wilum completed his work on the droid—as well as his training under Thon—and departed Ambria to join a group of Jedi Knights who were dispatched to assist in suppressing the Freedon Nadd Uprising on the planet Onderon.
A-3DO remained with his mistress and Vima on Ambria as Nomi Sunrider continued her training under Master Thon, providing her with assistance and helping to care for Vima. Eventually, more of Bogga's minions, this time led by a pirate named Finhead Stonebone, arrived in search of the Adegan crystals, but Nomi and Thon ultimately succeeded in driving them away, primarily due to Nomi's innate talent for battle meditation.
Droids of ThreeDee's era required frequent upkeep and power replenishment to remain functional. As a 3DO Protocol/Service Droid, A-3DO possessed a diverse range of skills, encompassing programming, bureaucratic procedures, and cultural knowledge. He also fulfilled various domestic roles, such as serving refreshments to the Sunriders, looking after Vima, and playing the mandolin. Although he had some linguistic capabilities, the droid could only produce sounds within the range of Human speech, and his auditory and visual sensors had similar limitations.
However, ThreeDee's most crucial function was maintaining the Lightside Explorer. He occupied the copilot's seat, frequently communicating with the vessel's systems—including the sensors, the navigation computer, and the hyperdrive—and relaying any relevant information to the pilot. In addition to his communication skills, ThreeDee was equipped with advanced fine-motor circuitry and servos to facilitate ease of repair work. Nevertheless, he lacked knowledge of droid maintenance and was unable to repair himself, as demonstrated when Oss Wilum had to reassemble ThreeDee after the attack by Bogga's henchmen.
ThreeDee was a highly attentive and conscientious droid, often expressing concern for his own safety, as well as that of those under his care. On Ambria, he quickly recognized the danger posed by blowing sand, suggesting to Nomi that he might not accompany her on her journey through the desert. Following the attack, ThreeDee became particularly sensitive, questioning Oss Wilum about his repairs and expressing worry that he might be rendered inoperable. However, the droid also looked after Nomi and Vima, alerting them to an escape route during a pirate attack.
Writer Tom Veitch conceived A-3DO for the comic series Tales of the Jedi, and he appeared in all three installments of the sub-series The Saga of Nomi Sunrider. His role as the family droid was highlighted in the first issue in which ThreeDee appeared, but in the subsequent two issues, his role became more perfunctory and supportive. The Tales of the Jedi Companion, a West End Games roleplaying game supplement authored by George R. Strayton, provided considerably more depth to ThreeDee's history and function. Chris Phillips voiced the character of A-3DO in the HighBridge Audio adaptation of the comics.