Born in 2303, Juliana O'Donnell lived at the Omicron Theta colony. She met Doctor Noonian Soong on the colony, and the two fell in love. However, her mother disapproved of their relationship due to the age gap, so they met in secret. They boarded the SS Wisconsin in 2328 to get married in secret on Mavala IV. Though they had no biological children, she treated each of the Soong-type androids as if they were her children.
Juliana assisted Noonian Soong in his work on artificial lifeforms, and helped create the android Data, as well as his four predecessors, including Lore and B-4. Juliana viewed each android as akin to a child; after Lore's personality problems forced his deactivation, she was incredulous that Noonian wanted to try again. When creating Data, Juliana was responsible for giving Data the capability to later play music and paint, as well as other creative outlets, feeling that he deserved a chance to express himself even if he lacked the emotional capacity to explore that side of himself.
When the Crystalline Entity attacked the colony in 2338, the Soongs fled the planet. Juliana, fearing that Data would eventually become unstable like Lore, insisted that he be left behind, though this caused her great guilt. The two made their way to the Terlina system; however, Juliana had been seriously injured in the attack, and fell into a coma.
Unable to stand the thought of losing the only woman he ever loved, Noonian built a new android and transferred his wife's memories into it, using a synaptic scanning technique. He made several modifications from his earlier androids: skin with the appearance of veins, capillaries, tear ducts, and sweat glands. The appearance of the skin and hair would change over time, something already part of Data's design, to be consistent with a Human of Juliana's age. He also included a feedback processor that sent out a false bio-signal, self-adjusting to mimic Human aging. She was programmed to eventually terminate, giving her the appearance of a natural death. Juliana was designed to be unaware of her android nature and programmed to shut down if the truth about her android body was ever discovered. She was fitted with an internal information module with a holographic interface so a holographic program of Noonian could answer any questions people may have about what happened to her. The program responded variously depending upon the identity of whoever was accessing it. A few days after Juliana's death, Soong activated the android.
When Noonian activated her, he recalled that "she looked up at me and smiled. She recognized me. It had worked! Here was a life not two minutes old, and as far as she knew I was her husband. She'd just recovered from a terrible injury. It was incredible." The relationship between the Soongs continued for a while, eventually souring due to the isolation of Terlina III, and Dr. Soong's failure to adequately express his love for her. Juliana left Noonian – something that Noonian noted the 'original' Julianna would have done as well, although she would also tell Data that she would come to realize and acknowledged that Soong loved her as much as his work. She eventually made her way to Atrea IV, where she met and married the Atrean scientist Pran Tainer, becoming his assistant.
In 2370, the USS Enterprise-D arrived at Atrea IV to assist in planetary core experiments. Data and Juliana were reunited, although Data was unaware of her possible role in his life as his formative memories of those days had been erased. Although Data was initially uncertain about how he should feel about Juliana's claims regarding her role in his initial design and early development, a conversation with Geordi La Forge convinced him that he should not avoid Juliana due to his inability to remember her. From this point he began to spend time with Juliana, addressing her as his mother. Data and Juliana bonded over their mutual creative outlet, Data playing violin and Juliana, the viola. Juliana shortly revealed that she was responsible for leaving Data behind on Omicron Theta because she was afraid of him turning out like Lore.
During the mission, Juliana was injured and her true nature as an android was discovered. Data noted that he had observed clues about her android nature before this point, such as that the intervals between her blinks were governed by the Fourier system, the same mathematical formula Dr. Soong used to give Data blinking pattern the appearance of randomness, and as well, her viola performance was identical to her practice.
Data interacted with the personalized version of the Soong holoprogram meant for himself, which ultimately asked him to not reveal the truth to Juliana. From this, Data chose not to reveal her status as an android to her. Data's decision regarded the happiness he believed she obtained from her belief in her humanity. Data prioritized this over whatever satisfaction he may have received in the shared knowledge of their android nature, although he noted that had he come to the conclusion that knowing the truth would have been the best path for her and her wellbeing, he would have done so in spite of Soong's wishes. Before Juliana departed, Data told her that Noonian Soong had once told him that he only ever had one great love in his life, expressing his certainty that she was the object of that love. (TNG: "Inheritance")
|First two • B-4 • Lore • Data • Juliana Soong • Lal|
Juliana Tainer was played by actress Fionnula Flanagan and doubled by stuntwoman Christine Anne Baur. Flanagan's greenish costume from "Inheritance" was later sold off on the It's A Wrap! sale and auction on eBay and was also worn by background actress Faith Burton in the Star Trek: Voyager seventh season episode "Drive".  Christine Anne Baur's Juliana Tainer costume was also sold off on eBay. 
In the script of "Inheritance", the character was described as "a fiftyish [Human] woman dressed in Atrean fashion."  The okudagram of Juliana's medical records indicate that she is 67 years old in 2370. The name "Juliana Tainer" was chosen by co-writer Dan Koeppel, after mountain bike racer Juli Furtado. 
The novel Immortal Coil establishes that Juliana eventually did seem to die in the year 2374, only to be reactivated with full knowledge of who and what she was by the immortal known as Flint. In the novel Cold Equations: The Persistence of Memory, Data learns of Flint's role in reactivating Juliana, deciding to try to find him so that Flint might help Data reactivate Lal.