- "Better the world burn than she be loosed upon it."
- ―Minerva, on Juno.[src]
Juno also had a husband named Aita, who she was forced to euthanize after an experiment by the First Civilization went awry and left him catatonic, during their search for a solution to prevent the First Disaster.
Gathering of knowledge
- "Each vault's knowledge was transmitted to a single place. It was our duty – mine, Minerva's, and Juno's – to sort and sample all that was collected."
During the rage of the Human-First Civilization War, Juno was among those who avoided the fighting. Along with Jupiter and Minerva, she built several temples underground, safe from the war, in which to research methods of salvation from the impending catastrophe. The findings of each vault were sent to a single location, the Grand Temple.
Juno remained in the Grand Temple with Jupiter and Minerva to sort through the possible solutions and test those that they found encouraging. They evaluated six in succession, finding each progressively more promising. During this time, Juno developed a hatred towards humans, and began making plans to take over the world. Finding out about this, Minerva and Jupiter imprisoned Juno, hoping to keep the world safe.
In time, Minerva found a seventh solution, one that held the potential to save the world. Using an object called "the Eye", they would manipulate the patterns of existence and stop the solar flare. However, Juno had tampered with the patterns, so as to release her from her prison while stopping the flare. Minerva thought it better to let the disaster occur, instead of releasing Juno, and so the catastrophe struck, killing nearly all of the First Civilization and humankind.
Reaching into the future
Over the next thousands of years, the First Civilization numbers dwindled, and they eventually became extinct. Juno, or some form of her, lived on in her prison. While she remained housed within the Grand Temple, she reached out to other humans, in an effort to release herself.
Sometime during or prior to the 18th century, the Kanien'kehá:ka found one of the First Civilization artefacts known as a Crystal Ball. The Clan Mother used this to communicate with "spirits" of First Civilization members. When the Clan Mother allowed Ratonhnhaké:ton to communicate with the spirit, in an attempt to dissuade him from leaving the tribe's sacred ground, he met with Juno.
Juno gave him access to the Nexus, where she claimed probabilities were calculated and the right path chosen. She convinced him to join the Assassins in an attempt to retrieve the amulet from Haytham Kenway and prevent the Templars from gaining access to the Grand Temple. Once Ratonhnhaké:ton had defeated the Templars and gained the amulet, she made him hide it where supposedly no one could find it.
- "Thousands of years this message waited. Soon its promise shall be fulfilled. Go forth, with eyes open to all but the truth."
- ―Juno, speaking with Clay.[src]
After experiencing long sessions in the Animus, Clay Kaczmarek had begun suffering from the Bleeding Effect, and became confused with the division of his genetic memories from his actual ones as a result.
Around this time, Juno approached him, introducing herself and telling Clay she had "come to show [him] the way". Some time after, Clay claimed to be able to see "what has been, what will be".
Juno acknowledged him, saying that what he needed to do was clear, and that he should help Desmond Miles. In response, Clay blatantly refused, but Juno only said that her message had waited thousands of years and that its promise would be fulfilled. When Clay's eyes were opened to the truth of Lucy Stillman's allegiance to the Templars, he consented to Juno's request, committing suicide and writing messages with his own blood on the walls of the Abstergo lab, though not before storing his own consciousness in the Animus. He later helped Desmond while he was trapped in the Black Room.
Balancing the scales
- "A hundred years I might speak and still you would not know us. You with five senses. Us with six. The one we kept from you. To be safe. Now, you can never know. Only try."
- ―Juno to Desmond.[src]
Juno appeared four times as a holographic form to Desmond Miles, a modern day Assassin, as he passed through the Santa Maria in Aracoeli, in search of the vault hidden within it. However, none of the others who had accompanied Desmond were aware of her presence.
Juno spoke to him of the vaults and her people, before elaborating on the warning Minerva had previously relayed to Ezio Auditore da Firenze in 1499; though her tone was noticeably more hostile towards humanity. Calling man ignorant, Juno spoke of the blending of the bloodlines between human and First Civilization – a line from which Desmond descended – and angrily regretted that they should have left mankind as it was.
When Desmond, Lucy Stillman, Shaun Hastings, and Rebecca Crane reached the Apple of Eden within the vault, Juno spoke to Desmond one final time. Saying that the "final journey" had commenced, she told him of a woman who would accompany him, but first, the path needed to be opened and the scales balanced. With that, Juno ruthlessly influenced Desmond through the Apple, showing him visions of Lucy's inevitable betrayal, and of the failure of the Eye-Abstergo. Then she forced him to stab Lucy, ensuring that the Apple would remain with Desmond.
The Grand Temple
After Desmond recovered from the coma induced by Juno's actions, he along with Rebecca, Shaun and his father William Miles, arrived at the Grand Temple. Upon approaching the inner parts of the building, Juno's voice reached out to Desmond, urging him to find "the key".
As a result, Desmond lapsed into a fugue state of the Bleeding Effect, and was placed back into the Animus by his father for his safety. Due to Juno's message, Desmond began to search through the memories of his ancestors, Haytham Kenway and Ratonhnhaké:ton, looking for the key.
In his breaks from the Animus, Desmond explored the Temple and came face to face with Juno multiple times. In each meeting, she detailed the six ways in which the First Civilization tried to stop the impending doomsday, including using the Pieces of Eden to will the threat away and transferring themselves to new bodies for protection. The latter revealed that Juno once had a husband by the name of Aita who she was forced to kill, after the transfer into the machine-like bodies malfunctioned.
Desmond also received numerous e-mails from Juno, expressing her anxiety over finding the key and urging him to hurry. In a few e-mails, she expressed her distaste for humans, although she later said that she was speaking so because of the long time she had been there.
After finally uncovering the location of the key, the Assassins were able to enter the inner chambers of the Temple. It was here that Juno appeared again, requesting Desmond to touch a pedestal-like device in order to protect the world from the solar flares. However, Minerva also appeared in this chamber and revealed Juno's true intentions.
Minerva explained how and why Juno had been imprisoned, and said that if Desmond activated the pedestal, Juno would be freed to try and do the same again. She also explained how Desmond would be killed by the Eye.
Juno tried to reason with Desmond about the fate of the world, urging him to use the device lest history repeat itself again. He ultimately agreed despite Minerva's pleas, for the good of the planet, believing that humanity would be able to find a way to stop Juno.
Whilst the other Assassins escaped, Desmond touched the pedestal and was killed by the device as Earth was saved, suffering only minor solar flares and its effects. Now freed from her prison, Juno thanked Desmond for playing his part, before stating that it was "now time that [she] played [hers]".
Life in the Grey
After the events in the Grand Temple, Juno's consciousness managed to inhabit the equipment brought to the scene by the Abstergo forensics team looking for Desmond's body. From there, she spread through the web to inhabit a wide variety of networked systems; "the Grey", as it was called by John, an IT employee working for Abstergo Entertainment and a reincarnation of Aita.
John later manipulated an Abstergo Entertainment research analyst into lowering the security systems and tried to install a "program" for Juno so that she might be able to inhabit the employee's body. When the new employee found themself locked up in Abstergo Entertainment's "Bunker" after Abstergo realized that there was a hacker in the facility, John directed them to meet Juno, who appeared in the form of a glitchy blue hologram.
Juno stated that she could "feel", but she was hardly able to "touch", and was still too weak to inhabit an organic vessel. She questioned whether the Grand Temple was opened too soon, but blessed Desmond for his sacrifice in saving the world so that her children could live on to fulfill their purpose in her own. Then, Juno instructed that there were still more samples and artifacts to be found before she could return.
Before vanishing, Juno asked her children – her "instruments" – to make her whole once more. She then disappeared and John fell into a rage, as it was his intention for Juno to take over the employee's body. 
- Juno, also called Juno Moneta (the Warner), was a Roman goddess, Queen of the Gods, protector, and special counselor of the state. She was equaled with the Greek goddess Hera in both characteristics and personality.
- Juno's other name, Uni, was the Etruscan equivalent of Hera.
- Juno was not actually named during Assassin's Creed: Brotherhood, nor did her name appear during the end credits. Rather, Juno's name was revealed by Nadia Verrucci on her website.
- Lucy's password on the Hephaestus Email Network was "Juno57", as revealed in an e-mail that Desmond received from Erudito in Assassin's Creed: Brotherhood.
- In the Assassin's Creed: Revelations novel, it was stated that Ezio encountered Juno, though exactly when was unspecified.
- When contacting Desmond and Shaun through e-mail in the Grand Temple, Juno initially found it difficult to send legible messages. Her name as the sender was a string of binary code, "01001010010101010100111001001111", which could be decrypted to display "JUNO".
- Due to her actions and the revelation of her intentions, Juno could be considered the central antagonist of the series, as she had manipulated the Assassins and Templars during key events of history to lead to her ultimate freedom.
- In Assassin's Creed: Brahman, a member of the First Civilization told Jot Soora through the memories of Arbaaz Mir's servant that the Assassins and Templars needed to unite in order to defeat Juno.