All information is taken from Memory Beta.
Erika Hernandez was a Human female in the 22nd century, who enlisted in United Earth Starfleet, reaching the rank of captain and made commanding officer of Earth's second Warp Five-Capable Starship; the Columbia (NX-02).
In the beginning of her career, Erika became romantically involved with her fellow officer Jonathan Archer, though were forced to break off their relationship when Archer was promoted, making it inappropriate for Erika to be with a superior officer.
The details of her previous assignments to Columbia are unknown, but, immediately prior to the posting, was assigned to the Republic as its executive officer under the command of Captain Jennings. When Erika left, Jennings allowed her to take the ship's cook with her.
In 2153, Erika reached the rank of captain and took command of the NX class starship Columbia. In February of 2154, the Enterprise (NX-01), under Archer's command, returned to Earth from it's mission to stop the Xindi destroying the planet. Erika met Archer at the Starfleet officer's favorite bar, and immediately sought his advice on sorting out the final details of her ships' equipment and crew.
When Archer was ordered by Maxwell Forrest to take a vacation (when the stresses of the Xindi mission began taking their toll), he went rock climbing. Erika followed and readily offered her companionship and solace. With time, Erika helped Archer open up and express his feelings, especially the hurt and anger he had contained over the immense ordeals and problems he and his crew suffered near-constantly during the past year. At this time, Erika and Archer, now the same rank, rekindled their romantic relationship and made love. They did, however, decide to keep their relationship a secret.
The Columbia's launch was continuously delayed due to technical problems, so Erika twice tried to convince Enterprise's chief engineer Charles Tucker to transfer to her ship. For personal reasons, Tucker ultimately accepted, and with his knowledge and experience, Columbia finally launched a year after it's original date.
Not long afterwards, Erika and her crew came to the aid of Enterprise when it faced destruction due to Klingon sabotage. The ships performed an impressive maneuver that merged their warp fields, allowing Tucker to reach the Enterprise, using a tether connecting the ships together. Once safely aboard, Tucker corrected the engine's sabotaged computer systems, saving the Enterprise.
The Columbia joined forces with Enterprise during its mission to rescue Doctor Phlox, and as such protected Qu'Vat colony (where Phlox was attempting to create a cure to the Klingon augment virus, and Columbia fought off Fleet Admiral Krell, who, along with his fleet were attempting to prevent the virus' spread by sterilizing all infected planets. Erika successfully assisted in holding off the Klingons until Phlox resolved the situation, saving countless millions of lives. It was at this time Tucker decided to return to Enterprise, with Erika approving the transfer.
In 2156, the Columbia was assigned to escort a convoy when they were attacked by the Romulans. With the convoy destroyed and the Columbia's warp drive offline, Hernandez ordered the use of the Columbia's impulse engines to make a journey to reach the nearest class M planet with any sign of technology, during which the vessel and all aboard experienced time dilation effects - while the journey took them twelve years in normal time, the crew of the Columbia experienced a passage of only sixty-three days.
Arriving in 2168, Hernandez commanded the landing party to the planet Erigol that made first contact with the Caeliar race, liasioning with Inyx. After efforts by Major Stephen Foyle and other members of the team to use the Caeliar's technology to return the Columbia to it's original time went badly wrong, the city-ship of Axion, including Hernandez and three of her crew, was relocated in time to the year 1519. (ST - Destiny novel: Gods of Night)
Erika was summoned to the Quorum Hall to speak to the Caeliar ruling Quorum, and she insisted upon bringing first officer Veronica Fletcher with her. After being informed there was no way to return to their own time, the four former officers were given permanent residences in the city, disallowed from ever leaving the Caeliar and ruining their isolation. Erika found that the first thing she lost was her concepts of time; without a star to tell days, she lost track of time. At the urgings of the Caeliar, the officers tried their hands at many forms of art; Erika found she had little skill in any of her attempts at music, sculpture, painting, drawing, or singing. Instead she began working with Caeliar scientist, Inyx, learning about Caeliar technology and assisting within the Star Chamber in finding a new planet to set down the city-ship. At one point, she offered to take her officers to scout potential planets, but Inyx disallowed this option, suspecting that they would attempt an escape. Her assistance with the Caeliar began to drive a wedge between her and her former officers, who saw the Caeliar as nothing more than captors.
Communications officer Sidra Valerian slowly became mentally unstable, requiring constant care from Johanna Metzger. Hoping a more natural environment would improve the conditions of the entire team, Erika Hernandez had Inyx and Edrin of the Caeliar construct a holochamber of a beach; she was pleased with the results and Valerian found joy in the ocean, but the other two dismissed it as an attempt to win over their friendship. After Metzger committed suicide in 1573, Valerian's condition worsened and she sank into a cataonic state, where she neither ate nor drank. Although Erika originally allowed her body to waste away, she became stricken and asked the Caeliar to find a way to heal her friend. Hernandez allowed the Caeliar to perform an experimental procedure on her, attempting to link her mind with the Caeliar communal gestalt, despite the protests of her first officer. The procedure failed and Valerian died on the operating table while Hernandez and Fletcher looked on. Already concerned about her captain's friendship with Inyx, the failure strained the relationship between Hernandez and Fletcher further. Sensing the great loss, Erika left the operating area in shame, and traveled to a far part of town to sit under a tree where her away team had regularly met when they first arrived. Hernandez and Fletcher did not interact for nearly a year, until Fletcher had come to terms with her feelings and her own mortality. During this time, Erika continued to assist in locating a planet, and learned the Caeliar's written language. Coming back to their home after work, Hernandez found Fletcher awaiting over a game of chess, where Fletcher allowed Hernandez back into her life, and revealed she was dying.
A short time later, the city-ship of Axion set down on a new planet in late 1574, which was named New Erigol. As soon as the city was down, Fletcher asked to depart and scout the planet, choosing her own gravesite on the surface. Once the Caeliar had begun to settle, Edrin supervised the construction of a house for the two of them, where they lived together for nearly six months. One morning, Fletcher did not appear for morning meal, and Hernandez went looking for her and found her dying in her bed. She summoned Inyx, hoping they could help her, but Fletcher had left explicit instructions to not interfere with her natural death. He transported them to the gravesite where Fletcher died; Hernandez opted not to say anything more before her body was interred.
With her three friends all dead, her mental condition worsened. After six days alone in the house, she had it razed and returned to the city. After continuing to assist the Caeliar, she discovered they were building a shell around the planet and sun, and she would be without natural sunlight. She attempted suicide by throwing herself down a large flight of stairs, but she ended up only severely injuring her body, and she awoke in Inyx's operating facility. She asked to be allowed to die, but Inyx insisted that her continued life gave him great confort and companionship, and he would be greatly saddened if she died. He revealed that despite the sanctions of the ruling Quorum, he had continued the research into methods to link humans with the gestalt, a procedure that Hernandez agreed to undertake.
Despite the previous failure with Valerian, the procedure was a success, and she was linked with the Carliar. However Hernandez soon realized that although her link to the Caeliar gestalt had both restored her youth and granted her several new abilities via the catoms in her body, she was also required to stay within the quantum field of Axion for the catoms to function – effectively making herself a prisoner on New Erigol forever. She discovered that her physiological changes resulted in the loss of her need to sleep or eat, as the catoms provided her body's every need. Her memory improved, and she found an improved ability to paint. Inyx had the city of Axion moved so that she would not see Fletcher's gravesite all the time.
Over the next six hundred years, Hernandez devoted her time to learning all she could about Caeliar technology and also attuning herself to the gestalt – a fact she deliberately kept hidden from Inyx, even though she could not fully understand their spoken language. She also learned, through the gestalt, that should she leave New Erigol, she would not die immediately, but would simply begin to age normally again as the catoms in her body no longer replenished her. Upon learning this, she began planning an escape. She also attempted to observe Earth history; her attempts were discovered and she was brought before the Quorum. Ordemo Nordal chastised her, and ordered Inyx to keep a closer watch over her, as he would be held responsible for her further actions.
In 2168, once there was no longer a danger of polluting the proper timeline, Hernandez attempted her first communication off the planet. She encoded a SOS along with a Fibonacci sequence for transmission in one of the soliton pulses, but it was caught and blocked by a filter Inyx had installed. Over the next two hundred years, she continued to refine her methods and techniques. She located a backup node in the soliton network and rewired it to be a primary emitter; Inyx revealed it to be a ruse in order to distract her and had it deactivated before she could transmit. She then begun construction on her own emitter, building the pieces in secret and keeping each item in isolation until she was ready to bring them all together. As she activated it, Inyx appeared and destroyed it, an act that caused her a great deal of sorrow and anger, despite knowing why the Caeliar revered the secrecy.
In 2381, a new opportunity presented itself when the USS Titan entered orbit of New Erigol and sent down an away team. Hernandez acted as a liaison to the away team, and found herself sympathising with them.
ransporting herself to the Titan, Hernandez offered Captain Will Riker a chance to return to United Federation of Planets space, even though it would mean leaving his away team behind. Riker accepted and Hernandez activated a subspace tunnel, transporting Titan to the Azure Nebula. Inside the nebula, Titan rendezvoused with the starships Aventine and Enterprise, and Hernandez met Captains Jean-Luc Picard and Ezri Dax. Initially suspicious of Picard, she revealed that she had heard the voice of the Borg Collective via her catoms and recognised him as the one called Locutus of Borg. Based on this knowledge Hernandez and Dax devised a dangerous plan to intercept and board a lone Borg scout vessel and to physically 'plug' her in to the vinculum where she could use her catoms to broadcast her thought patterns on the same frequency as the Borg Queen – impersonating her 'voice.' The plan was a partial success as Hernandez was able to cause the Borg fleet to begin fighting among itself. As a result the vessels attacking Vulcan, Beta Rigel, Qo'noS, Andor and Coridan were routed; however Hernandez was not strong enough to maintain control of the collective and the Queen soon reasserted herself.
After escaping from the scout ship, Hernandez explained to Captain Dax that, based on her experience with the Collective and her analysis of the Borg nanoprobes, she believed that the Borg originated through a botched version of the Caeliar/Human hybridisation process. This revelation led to the formation of an even more dangerous plan – to lure all the remaining Borg ships back to the Azure Nebula using the Omega molecule generator used to power the Caeliar city-ship, Axion – and to allow the Caeliar to liberate the entire Collective. Upon its arrival, Hernandez returned to Axion, in exchange for the return of the Titan's away team, and was able to convince the Caeliar gestalt of both the responsibility and necessity of aiding her in the plan. She then transported herself to the Borg Queen's ship and allowed herself to be assimilated. However, the Caeliar's collective consciousness was stronger than the Collective and soon, through Hernandez, they were able to take control and finally liberate Sedín, who's corrupted essence, ravenous hunger and desire to perpetuate its own existence had driven the Collective for six millennia. With its consciousness gone, the bewildered drones were embraced by the gestalt, and the Caeliar became a polyglot society – which included Erika Hernandez – who was finally able to admit she was a Caeliar.