- "Basically, I think the Assassins and Templars are both wrong."
Sebastian Monroe was a former high-level researcher of Abstergo Industries and member of the Templar Order before he left for mysterious reasons, stealing various technologies in the process, including an Animus.
Monroe field of expertise at Abstergo were the "Ascendance Events"; various bloodlines crossing through centuries, being in contact with Pieces of Eden, until they all met at some point as if the generations where guided toward that moment by an unidentified force.
Monroe had a very traumatic childhood, which later made him unfit to use the Animus, his abused psyche being too unstable to safely use the device.
While working for Abstergo Industries, Monroe discovered a subcode in the DNA behind the primary code. Once he knew what to look for, he discovered fragments of the subcode and, desiring to understand its mechanics, ran protosimulations to see what would happen. Mere curiosity turned into obsession, Monroe made it his mission to recreate the entire collective unconscious sub-DNA. He also discovered the existence of the Ascendance Event, which he came to believe was a source of wisdom. However, he made the mistake of mentioning it to Isaiah, who became obsessed with it as well, believing it would grant him power.
The IT guy
After being forbidden by Dr. Victoria Bibeau to look into the memories of his abusive father to exorcise his demons, Monroe became erratic and stole an Animus. Hiding from Abstergo, he then posed as the IT guy in various schools discreetly offering Animus sessions to teenagers looking for thrills or seeking answers that went against their expectations. In fact, Monroe was looking into their DNA for Assassin/Templar descendants as well as fragments of the sub-DNA, and by 2016, had found several subjects: Natalya Aliyev, Sean Molloy, Grace and her brother David Collins.
That same year, Monroe found two new subjects, Owen Meyers and his friend Javier Mondragón. Owen believed he could use the Animus to prove his late father's innocence in a robbery from 2001, but Monroe told him he only possessed his father's genetic memories until before his conception and that he would need his father's DNA from after the robbery. Despite being unable to help Owen, Monroe offered him and Javier use of the Animus, finding Genetic Memory Concordance. Through them, Monroe discovered clues about the Trident of Eden, once they had inadvertently confirmed that Hernán Cortés possessed a Dagger of Eden. After pulling Owen and Javier from the Animus and parting ways, Monroe resigned from his current IT job and disappeared.
Monroe later came to Owen's rescue when he was accosted by a Templar agent seeking to recruit him in exchange for helping exonerate his father, only for the Templar to be taken out by the Assassin Griffin. Using advanced tech in his Abstergo bike, Monroe was able to outpace Griffin when he attempted to pursue them.
Looking for the Trident
The first prong
Monroe brought Owen to a warehouse, where he had gathered Javier and the other teenagers. Telling them about the Assassin/Templar millenary feud, Monroe convinced the group of teenagers to work with him, to find the artifact and according to him to hide it from both the Assassins and Templars, promising both groups would leave them alone. Relieving the memories of their ancestors from the draft riots of 1863 under the guidance of Monroe, the teenagers discovered that a piece of the trident was last seen in possession of General Ulysses S. Grant.
However the use of the Animus didn't go unnoticed and a Templar strike team captured the teenagers with only Owen and Javier escaping thanks to the Bleeding Effect while Monroe disappeared with the Animus core. While Grace and Sean decided to trust the Templars, Owen and Javier worked with the Assassins, but as both the factions converged to Grant's house in Mount McGregor, they discovered that someone else already took the first prong of the Trident and left.
Once Monroe made it as far as he could and recuperated, he berated himself for being so careless and vowed to rescue the teenagers from the Templars. To that end, he used a burner phone he purchased to call Cole, a Templar who owed him a favour.
Attempted rescue and capture
With Cole's aid, Monroe infiltrated the Aerie, where everyone excluding Owen and Javier were being kept, disguised as an Abstergo agent. He then caused a fire that caused a blackout to unlock the teens' rooms. He eventually found Grace, David and Natalya. When told that Sean wanted to stay, he chose to accept his choice. Upon hearing Grace telling him he shouldn't have come for them, Monroe guessed that Isaiah told them a half-truth about him and informed them that Isaiah was a master manipulator. David and Natalya then chose to leave with him but before Grace could make her choice, the power came back on, separating her from the rest of the group. With little time to lose, Monroe led Natalya and David to the garage, where Templar agents started firing on them. They were soon joined by Owen and Javier, who had joined the Assassins in an independent rescue attempt. Owen then stayed behind to provide covering fire while Javier took Natalya and David to safety, stealing Isaiah's high-tech stealth car in the process. Monroe stayed behind for unknown reasons and, when Isaiah entered the garage and announced that he had reinforcements on the way, Monroe surrendered himself and urged Owen to do the same.
The second prong
However, Monroe was not held captive long. With Isaiah preoccupied leading an expedition to Mongolia, where the second prong was buried, Cole made arrangements for Monroe to be shipped to Mongolia in a cargo container, and had caught Owen and Grace attempting to spring him. Once the trio were safely inside the container, Cole told Monroe that her debt with him was squared. After sealed them in, Owen asked Monroe if Cole was Rothenburg, an Assassin informant inside Abstergo, to which he told him not to ask questions that might put Cole in danger.
During the journey, Monroe caught up with the two teens on what had been happening with them and was surprised to hear that they assumed he had taken the first prong. He then asked if Isaiah mentioned the Ascendance Event and, at Owen's request, explained what he knew of the Ascendance Event and the sub-DNA, revealing that all six teens make up the whole of the sub-DNA.
Upon their arrival in Mongolia, they are soon discovered by Isaiah and captured. Subsequently, the Templars spotted survivors from a crashed Assassin plane and were prepared to take it out when Grace, fearing her brother was there, told Isaiah to set off a series of lights to lure David in so he could give Isaiah the location of the tomb. Once David was captured and interrogated by Isaiah, he claimed that the tomb of Mongke Khan was south of the Templar camp. After Isaiah had left, Monroe asked David why he would betray the tomb's location, to which Owen retorted that it was better than the Assassins getting their hands on it. Monroe then learned that Owen had gotten a sample of his father's DNA and Isaiah allowed him to use Helix, which showed him the Assassins using his father in the bank robbery that sent him to prison. However, Monroe insisted that Isaiah falsified the memory to show Owen what he wanted to see, but Owen stubbornly refused to believe it.
Soon after, David got a guard to let him use a portable toilet, before Owen and Grace swiftly disabled the second guard, to Monroe's surprise; they explained that they feel strong Bleeding Effects in each other's presence. They proceed to take down the remaining guards before finding David, who then led them to the tomb's real location, having misled Isaiah.
They later join up with Javier and Natalya, the latter having sedated the Assassins Griffin and Yanmei, and together they dig up the Khan's tomb, only for Isaiah to turn up, having let them believe he was tricked to find the tomb. Monroe pleaded with Isaiah not to hurt the teens, only to be told that he still needed all six of them. Though the Assassins recover and attack, Isaiah managed to get his hands on the second prong and unleashed its fear-inducing powers on everyone, managing to fatally wound Yanmei, before declaring his defection from the Templar Order. Afterwards, Isaiah left Monroe and the others.
With Griffin carrying Yanmei's body, the group made their way back to the Templar camp. When Natalya started blaming herself for not showing the Assassins the tomb beforehand, Monroe assured her she was not at fault. Subsequently, Victoria arrived at the camp, having just learned of Isaiah's betrayal and informs everyone that he had also acquired the first prong. When Victoria's bodyguards raised their weapons in alarm upon hearing that the Assassins were present, the teens reasoned that Isaiah was the bigger threat. Thus, Victoria and Griffin agreed to a ceasefire until they find the third prong and stop Isaiah.
Personality and characteristics
Though Monroe supports free will, he doesn't believe the Assassins share that belief, considering that their members swear loyalty and obedience to the Brotherhood. Additionally, he believes that even those who are of either Assassin or Templar descent are under no obligation to join one side.
Equipment and skills
Monroe has an eidetic memory. He is also a competent programmer who was able to modify his stolen Animus to allow multiple users to share their session while reliving their ancestors' memories (on the condition that each had an ancestor in the same area at the same moment). Monroe's Animus also gives a user more freedom in the simulation with less risks of desynchronization on the condition that they had more than one ancestor – such as a parent and their child – both in the same location during the relived event.