The Isu are an ancient and highly-advanced species of humanoid beings who were active on Earth during the eponymous era several millennia before the rise of even the most ancient human civilizations. The Isu are responsible for the creation of the Pieces of Eden, powerful artifacts and weapons that augmented their already superhuman abilities, as well as forming the human race itself.
Their history shrouded in mystery, the Isu ruled over Earth roughly 77,000 years ago, before they were largely wiped out, alongside their human creations, during the Great Catastrophe. By that point, the Isu had been in a decade long war with a human rebellion led by two hybrids, Adam and Eve, who sought to free humanity from servitude to their "gods".
Following the Great Catastrophe, the Isu population rapidly declined to the point of near extinction within the century, but their legacy would live on for thousands of years through myth and legend, becoming the focal point of many human religions, whether polytheistic or monotheistic. Further still, those Pieces of Eden that survive the Great Catastrophe also influenced early man’s development and eventually became a pivotal desire for both the Templar Order and the Brotherhood of Assassins, who waged a war of their own for control of the Pieces, and by extension humanity’s future.
Due to their long and storied history, and the legacy that their existence left, the Isu, as a species, were known by various names to humanity. Classified Homo sapiens divinus by Abstergo Industries, they were also interchangeably referred to as Those Who Came Before, the First Civilization, or the Precursors. Beyond this, certain groups of Isu, such as the Capitoline Triad, were believed by most human religions to be a part of a pantheon of gods.
Creation of humanity
Although the Isu were native to Earth and a product of thousands of years of evolution in their own right,  their exact origins are unclear. Minerva, an Isu and member of the Capitoline Triad, simply stated that her kind "came before" humanity and were responsible for the creation of Homo sapiens as a capable and docile workforce, albeit one formed in their own image.  Accompanying this, the Isu created Homo neanderthalensis—Neanderthals—whom they designed to be an expeditionary or military force.
While Minerva openly admitted that the Isu built humanity with the capacity to survive Earth's harsh environments, Juno made it clear that humans were not intended to be "wise", thereby ensuring they were to be obedient and resilient cattle to suit their creator’s needs.
Extensive research done by Clay Kaczmarek suggests that the Isu had radically altered the genetic makeup of a pre-existing species of primates on the planet to create humanity; as a result, this left a large gap with transitional species between archaic hominids and modern humans. By 1997, the Templars had become aware of this gap in humanity’s evolutionary development and believed that the best way to limit humanity's exposure to the possibility of the existence of the Isu was to arrange for fake skeletons to be planted in an expedition site in Ethiopia, merely to hold accountability for this evolutionary gap.
In order to enforce their control of humanity, various technologies were created by the Isu; the artifacts that mankind would later name "Pieces of Eden". It is believed that there were certain types of these Pieces that were able to tap simultaneously into a network of neurotransmitters located deep within the human brain, ensuring total obedience through means of remote mind control. However, there were some humans–the hybrids–who had been born without these neurotransmitters, which made them immune to the Pieces' mind control capabilities.
War and the Great Catastrophe
Having been instigated by the theft of an Apple of Eden by Adam and Eve, the human rebellion soon erupted into a full-scale war with the Isu. While the Isu were more technologically advanced and powerful, humanity possessed the advantage of numbers. The conflict lasted for a decade before abruptly ending when the Great Catastrophe–a coronal mass ejection from the Sun–occurred. The casualties on both sides were far greater than the Isu would ever have anticipated. The distraction of war had blinded them to all else, and their preoccupation with the conflict prevented them from seeing the signs of an impending danger from the "heavens" until it was too late.
A number of Isu scientists not devoted to the war effort had become aware of the imminent catastrophe, however, and endeavored to prevent it by thinking up various solutions so as to protect the Earth. The Capitoline Triad–consisting of Minerva, Juno, and Jupiter–decided to lock themselves away in the Grand Temple for years in order to test a variety potential solutions, following which they experimented with the most promising results in underground Temples spread across the globe. 
Despite this concentrated effort, however, none of the solutions developed were sufficient to protect even a fraction of Earth’s surface, or the populations thereon. Even the most promising solution would take tens-of-thousands of years to become viable.
Accepting that their fate was sealed, Minerva instead turned her sights to preventing the Catastrophe’s inevitable reoccurrence by making use of the Eye to analyse the patterns and equations of existence in order to leave hidden messages for future humans throughout time, in the hope that they would find these messages, and save the world from the catastrophe's reoccurrence. 
At the same time, Juno had also made plans for the world post-Catastrophe. Rather than save it, she sought to rule over it. When her plans were discovered, she was imprisoned by Minerva and Jupiter.
When it finally came time to use the Eye, Minerva discovered that Juno had tampered with it in such a manner that she would be freed from her imprisonment upon it being activated. Minerva made the decision to destroy the device rather than risk Juno's release, thus condemning the world to face a second solar flare, which would flip Earth's weakening magnetic field and reverse the polarity where it would make the planet become geologically unstable.
In the affairs of humans
- "For centuries Tinia and I walked the world, hoping to rekindle the spark of civilization. We shared what we knew as best we could."
- ―Minerva on rebuilding civilization, 2012.[src]
While both races survived the Great Catastrophe, few of either species number remained. Working together, they rebuilt their world, and while humanity continued to view their counterparts as gods, they no longer worked in servitude to them. Despite their survival, however, the Isu were unable to fully recover their numbers, and began an inevitable decline toward extinction.
Having now built a second Eye, Minerva recorded a number of holographic, yet interactive, messages to serve as a warning to those who entered the Vault under what would become the city of Rome. In it, Minerva warned of the impending doom, and spoke of how to prevent it. Concurrently, several other members of the Isu took independent steps to influence the thriving human race, attempting to put their knowledge to stone or parchment, though these did not withstand the test of time.. Barely a hundred years after the creation of the Temples, the Isu were almost completely extinct.
In 2012, while viewing the genetic memories of his ancestor Ezio Auditore da Firenze, the Assassin Desmond Miles came upon the first of Minerva's recordings. Convinced that they would need Ezio's Apple of Eden to locate the Temples, Desmond continued to relive his ancestor's memories, eventually tracking the artifact down to a vault beneath Santa Maria Aracoeli in Rome.
By October 2012, Desmond and his Assassin team had located the Grand Temple, where they discovered that in order to find the key that unlocked its inner barrier, Desmond would be required to relive the memories of his ancestor Haytham Kenway and his son Ratonhnhaké:ton. After some time in the temple, Shaun Hastings learned that the power sources for the Isu construct were running low and that the team needed to locate more. This prompted Desmond to venture out from the Temple to recover them, and on doing so, Juno showed him visions of the solutions the Isu had attempted as he replaced them.
After he fully relived the relevant memories of his ancestor, Desmond went forth to unlock the Temple's inner gate, where he found Minerva’s first Eye, which had been repaired by Juno while trapped within the Temple's walls. Juno herself then appeared to the group and told Desmond that by touching it, he would save humanity. She was interrupted by the appearance of Minerva, who had used the second Eye shortly before she died, allowing her a look into the future.
Minerva's projection warned Desmond that on touching it, the pedestal would indeed protect Earth from the solar flares, but would also release Juno into the world. She reasoned that it was better to let Earth burn than unleash Juno upon it.
Believing that the choosing to do nothing and let the world burn was worse than releasing Juno, Desmond denied Minerva's plea. He resolved that it was best to save the earth and hope that another might defeat Juno than to let countless lives be lost. Desmond then touched the pedestal and sacrificed himself, unleashing an aurora borealis-like shield around Earth that blocked the worst of the solar flares.
Following Desmond's death, Juno uploaded her consciousness from the Grand Temple to the equipment that was brought by Abstergo Industries to inspect the scene and preserve Desmond's body, led by team leader Case Fisher. She then transferred herself to the Abstergo mainframe, while Abstergo worked on using Desmond's genetic material to create a new initiative dubbed the Sample 17 Project, run by Abstergo Entertainment, to further explore his lineage.
During her natural lifetime, despite one plan to preserve their race resulting in failure, Juno enacted a fail-safe procedure, which allowed her husband Aita to continuously reincarnate in human form. This was enabled through the insertion of 'junk code' in the human genome, which would take over a fetus during development, allowing Aita's return to life. Multiple reincarnations of Aita, colloquially referred to as Sages, were able to exist at the same time, as was the case with Thomas Kavanagh, Jr. and Bartholomew Roberts.
By 2013, Aita had been reborn in the form of a Sage named John Standish, who worked as an IT technician at Abstergo Entertainment. Once a new research analyst came to work for the company to view the memories of Desmond's ancestor, Edward Kenway, a pirate during the eighteenth century, John sought to use their help in hacking the Abstergo information systems in return for advanced security clearance, while having the analyst pass on Abstergo's files and information to the Assassins Rebecca Crane and Shaun Hastings. It was also through Edward's memories that the analyst would learn of the Sage, Bartholomew Roberts, and his connection to an Isu complex known as the Observatory.
Despite this façade however, Standish was manipulating the analyst into giving Juno a body to inhabit. When the opportunity finally presented itself though, Juno stated that she was unable to take over the analyst due to the fact that she was scattered too thinly and that there were more artifacts to find and more samples to gather.
Enraged by his failure, John poisoned the analyst with a low dosage in a vain attempt to allow Juno to inhabit their body successfully, though he was interrupted and killed by Abstergo security personnel, with the analyst eventually recovering from the attack.
Following Standish's death, Abstergo began examining his remains and discovered his identity as a Sage. Within his genes, they found a high quantity of Isu triple-helix DNA, and began the Phoenix Project in the hope of sequencing the entire Isu genome in order to use the Animus technology and find out the race's scientific secrets, with an emphasis placed on the Pieces of Eden, throughout Isu history.
- "The rest is up to you, Desmond."
- ―Minerva to Desmond Miles, through the memories of Ezio Auditore da Firenze, 1499.[src]
As a species, the Isu are anatomically similar to their human creations though, unlike humanity, who were created with only five senses, the Isu possessed six; the sixth being referred to simply as 'knowledge'. The Isu are also a highly technologically advanced and powerful race who, through Minerva's Calculations, possessed limited precognitive abilities that allowed a select few Isu to predict, and attempt to influence, possible futures.
The Isu were also physically more imposing than humans, with some individuals standing a full 20 inches taller than humanityAlthough the Isu had a naturally longer lifespan, they were not immortal.
Following the Great Catastrophe, a concerted effort was made by a number of Isu to pass on, or awaken, this sixth sense to humanity, their "final, faltering hope". Ultimately, however, they failed; though humanity could "see the blue shimmer [and] "hear the words", they did not fully possess the 'knowledge' of their creators. This consequently convinced some Isu, like Juno, that humanity should have simply been left as they were.
- "They're gifts, Mr. Miles. From those who came before."
- ―Dr. Warren Vidic on the Pieces of Eden, 2012.[src]
Despite the mark they left behind on Earth, the Isu faded into obscurity rather rapidly after the Great Catastrophe. However, the inability of humans to comprehend their creators as anything but gods did allow for their names and characteristics to at least live on.
The lack of evidence for their existence did not prevent select groups of humans throughout time from uncovering their true nature, however. By the 12th century, the Knights Templar had a limited understanding of the nature of the precursor species.
The Templars also knew of the existence of the Pieces of Eden, and aimed to gather and exploit these devices to benefit their ideology, with Warren Vidic once referring to them as "gifts left behind". Indeed, the 20th century technology used to view the genetic memories of one's ancestor–the Animus–was based on technology utilized by the Isu to record genetic memories.
Minerva refuted this suggestion, however, simply stating that the Templars and Assassins had wasted time "squabbling over [the Isu's] refuse" rather than working together to protect against the Second Disaster. This situation was in significant contrast to that in the 15th century, where it had been the Assassins who knew explicitly of the existence of the Precursors, whilst Rodrigo Borgia, Grand Master of the Italian Templars, erroneously believed the Vatican Vault to be the location of God himself. This changed again, however, and five hundred years later the Order of Assassins knew next to nothing of the Isu's existence.
Though various religious belief structures seem to have been based on or taken influence from aspects and misinterpretations of the Isu, their existence was unknown to humanity at large. As early as the 12th century, the Knights Templar assumed that the focus of human religions, the gods, did not truly exist, and that miracles and other supernatural occurrences were simply manifestations of the powers of the Pieces of Eden. However, it is unclear if the Assassins and Templars understood the origin of the artifacts at that time.
The first known instance of a human becoming aware of the Isu's explicit existence following their extinction was that of Altaïr Ibn-La'Ahad, who made mention of them in his Codex. However, it would not be until the year 1499 that humanity would encounter the Isu again, when the Assassin Ezio Auditore encountered a hologram of a being calling herself Minerva in the Vatican Vault. Even though Ezio told his fellow Assassins of Minerva, they still did not understand her true nature, and Ezio himself showed great difficulty in understanding Minerva's explanation of her existence. By 2012, the Templars possessed a greater understanding of the true nature of the Isu, while the Assassins of this time held suspicions about them as well. These suspicions were later confirmed when Desmond relived Ezio's memories of his encounter with Minerva.
It is also apparent that they had connections with many of Earth's religions, and likely influenced their developments directly. During her warning to Desmond, Minerva made mention of her former names, as well as those of her fellow 'gods'; Merva, Uni, and Tinia, who later became known as Minerva, Juno, and Jupiter, respectively. Their former names corresponded to the Etruscan Triad of Deities, while the latter were the names of their Roman counterparts, who made up the Capitoline Triad. This shift in names may be indicative of why various religions have numerous similarities, as they all seem to be based on the story of the Isu.
Through Desmond's experiences, the Assassins became aware of three separate beings: Minerva, Juno, and Jupiter. They had previously been aware of a fourth being, Consus, as well, but it is unsure if the Order retained this knowledge up until the events of 2012. In the Grand Temple, they were also told of Juno's husband, Aita, whom she was forced to euthanize after an experiment for which he had volunteered went wrong.
- "Why do we have these gifts, these abilities? Because it's in our blood! [...] The seeds were planted as two worlds became one. Behold the Assassins, the children of two worlds!"
- ―Clay Kaczmarek, 2012.[src]
As part of their unique genetic makeup, the Isu possessed a triple-helix DNA structure and had six primary senses, as opposed to double-helix DNA sequence and five primary senses of their human creations. Another trait that distinguished the Isu from humans is that they were highly intelligent; the Isu were responsible for the creation of humanity. It is believed the Isu accomplished this task by genetically modifying several members of the Homo genus using the Pieces of Eden to make humans appear anatomically similar to the their creators, with the only differences being the height and the size of the skull.
Through the hybrids, however, certain human bloodlines adopted some of the increased skills and abilities of their creators. The individuals known as Tainted Ones, for instance, possessed increased strength and dexterity, and a resistance to the some of the affects of the Pieces of Eden.
William Miles later stated that one person in ten million would have a high concentration of Isu DNA. Clay Kaczmarek at one point theorized that the true reason behind the abilities of some Assassins was genetic, suggesting a lineage including both human and Isu blood. Clay's own genetic memories indicated him to be a direct descendant of both Adam and Eve, suggesting that his bloodline, if not many more, would all have access to these abilities. According to Abstergo, the average part of Isu DNA in regular humans is comprised between 0.0002% and 0.0005%, but in some individuals it can be higher, like for Desmond Miles–who had a count of 0.952%–or the Sages, who had a count of between 5% and 6%.
Indeed, a number of Desmond Mile's ancestors including Altaïr Ibn-La'Ahad, Ezio Auditore, Edward Kenway and his son, Haytham, and his grandson Ratonhnhaké:ton, all possessed Eagle Vision, while Ezio and Altaïr both exhibited proven resistance to the effects of the Pieces of Eden. Outside of Desmond's lineage, completely unrelated individuals like Giovanni Borgia, Aveline de Grandpré, Adéwalé, Shao Jun, Arno Dorian, Arbaaz Mir, and Jacob and Evie Frye, also possessed a natural affinity for Eagle Vision. In others, like Gavin Banks, it could be learned through great practice.
Additionally, Ezio's bloodline allowed him to properly use a Staff and Apple of Eden, combined, to open the Vatican Vault, while Rodrigo Borgia could not. Altaïr had previously used his Apple to enlighten the people of Cyprus to Armand Bouchart's lies, and Desmond Miles was able to make great use of the Pieces of Eden in order to enact.
Unidentified Isu members
- Though they played a greater part in the plot of Assassin's Creed II, the Isu were first mentioned briefly by Warren Vidic in Assassin's Creed. When talking to Desmond, Vidic claimed that the Templars were responsible for all major human technological advances in history, though he denied that they invented them, calling them "gifts... from those who came before".
- The story of the Isu, who created humanity as a docile workforce and subsequently viewed as gods by their creation, bears striking similarity to the Ancient Astronaut Theory, which is the idea that extraterrestrials visited the Earth in ancient times and genetically altered an existing hominid species to create humanity in their own image. As a result, extraterrestrials were responsible for influencing early human civilizations, cultures, and religions; and perceived as gods by their human creations.
- The only difference that this theory has to the explanation of the Isu is that the Isu did not come from outer space, having resided on the Earth and evolved over time.
- However, this theory can be supported by a hidden file in the audio of Assassin's Creed IV: Black Flag, where John Standish gives a monologue sarcastically congratulating the listener for finding said file. In it, he remarks about how much potential outer space has, and how the listener should have become an astronaut. It is possible other Isu members may have shared this view of space.
- During the transcript of Isu history, imagery could be seen of triangles that resembled the logo utilized by Abstergo Industries.
- Although Minerva stated she, Jupiter, and Juno were in charge of preventing the first coronal mass ejection, it has been also said that the Isu were too consumed by the war effort to notice the solar activity, making it seem like a majority of the Isu themselves were entirely unaware of the solar flare that was to come except very few scientists. Whether this is a writing error or the Isu scientists withheld information from the rest of their species is unknown.
- The word Isu is quite similar to the Egyptian word "jsw" which means 'Ancient(s)'. 
- Assassin's Creed (mentioned only)
- Assassin's Creed II (first appearance) (as projecion)
- Assassin's Creed: Renaissance
- Assassin's Creed: Brotherhood
- Assassin's Creed: Brotherhood (novel)
- Assassin's Creed: Revelations
- Assassin's Creed: Revelations (novel)
- Assassin's Creed: The Fall
- Assassin's Creed III
- Assassin's Creed IV: Black Flag
- Assassin's Creed: Brahman
- Assassin's Creed: Unity
- Assassin's Creed: Syndicate (first referred to as "Isu")
- Assassin's Creed: Origins
- Assassin's Creed: Odyssey
- ↑ 1.0 1.1 Assassin's Creed: Syndicate
- ↑ 2.0 2.1 2.2 Assassin's Creed: The Essential Guide
- ↑ 3.0 3.1 3.2 3.3 Assassin's Creed
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 Assassin's Creed II
- ↑ 5.0 5.1 5.2 Assassin's Creed Encyclopedia
- ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12 Assassin's Creed III
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Assassin's Creed: Brotherhood
- ↑ 8.0 8.1 8.2 Assassin's Creed: Unity
- ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Assassin's Creed IV: Black Flag
- ↑ Assassin's Creed: Odyssey – The Fate of Atlantis: Judgment of Atlantis – Welcome Home
- ↑ Assassin's Creed: Unity – Database: 15. Precursor Memo
- ↑ 12.0 12.1 12.2 Assassin's Creed: Project Legacy
- ↑ Assassin's Creed: Odyssey – Legacy of the First Blade: Hunted
- ↑ Assassin's Creed: Revelations
- ↑ Assassin's Creed III: Liberation
- ↑ Assassin's Creed: Initiates
- ↑ Assassin's Creed: Bloodlines
- ↑ 18.00 18.01 18.02 18.03 18.04 18.05 18.06 18.07 18.08 18.09 18.10 18.11 18.12 18.13 18.14 18.15 18.16 18.17 18.18 18.19 18.20 18.21 Assassin's Creed: Odyssey – The Fate of Atlantis
- ↑ Assassin's Creed: Odyssey
- ↑ Assassin's Creed: Brahman
- ↑ Assassin's Creed
- ↑ 22.0 22.1 Assassin's Creed: Revelations – Abstergo Files #20
- ↑ Assassin's Creed 4: Hawk
- ↑ Assassin's Creed 3: Accipiter
- ↑ Assassin's Creed 3: Accipiter
- ↑ Assassin's Creed: The Fall
- ↑ Assassin's Creed: Origins
- ↑ The Codex - Roots of the "Isu" Naming