Unnaturally intelligent and composed for a Brute, Atriox was the only known person in history to defy the Covenant and survive.
Forming the Banished
"Forty at a time, they carelessly sent them in. Forty, to break the front lines. Forty to die for beliefs not their own. None ever returned ... until he did!" Isabel explaining Atriox's early history and what eventually led him to defy the Covenant. Nothing is known about Atriox's early life, but along with the vast majority of kind, he was once a foot soldier in the Covenant military. Serving on the front lines during the Human-Covenant War, Atriox's clan according to Isabel, was predominantly used as expendable muscle - most likely due to a fearsome reputation and staunch belief in the Great Journey. Forty pack brothers at a time would be sent on suicidal missions in order to break the UNSC's frontline. None of these warriors ever returned, except for Atriox. Serving at a time before the Jiralhanae ascension within the Covenant hierarchy, Atriox carried out several of these suicidal missions, always returning as the sole survivor. Whilst this earnt him great respect and recognition from his peers, Atriox's growing hatred for the theocratic empire started to become noticeable. The loss of countless pack brothers, caused Atriox not only to question the treatment of his species but harbour resentment towards the Prophet's and eventually doubt the Great Journey, and purpose of the Human-Covenant war itself. Eventually, the San'shyum came to view Atriox as a potential threat and ordered him to be eliminated. Returning from yet another mission, Atriox found a group of Sangheili waiting for him. Surrendering his gravity hammer, Atriox dropped to his knees in front of the leader, apparently accepting his fate. When the executioner tried to stab him, however, Atriox defiantly caught the blade in his right hand and proceeded to kill led the Elite, claiming both his weapon and helmet. Enraged, the other Sangheili drew their own swords but at that moment, the surrounding Jiralhanae, including Decimus leapt to Atriox's defence. Massacring the Elites, the Brutes acknowledged Atriox as their leader, splitting away from the Covenant indefinitely, and thus The Banished were born.
Leading the Banished
Throughout the remainder of the Human-Covenant War, and prior to the Great-Schism, Atriox led the Banished into several conflicts with both the Covenant and the UNSC. Utilising guerilla warfare and the skills he had honed during his service to the Covenant, Atriox was able to successfully raid key strategic positions across the galaxy. With each victory, Atriox bolstered not only The Banished's armaments but its numbers as well. Xenos who felt they were being mistreated by the Covenant, blood-thirsty killers and mercenaries came to his side, though Atriox was also known for pressing others into his service. Post-Great Schism, Atriox would recruit Let 'Volir and his band of Sangheili mercenaries in the Banished, offering them fuel and supplies in exchange for their service thus gaining a fleet.
The Covenant, understandably, viewed Atriox as one of the greatest threats to its survival, alongside Humanity and the Flood. Yet for all their technological advancement, the Covenant never even came close to stopping Atriox and his Banished. The UNSC Office of Naval Intelligence, on the other hand, saw an opportunity. Recognising Atriox's existence and hatred of the Covenant, careful study of his character caused some to wonder if a mutual understanding or perhaps even an alliance could be reached with him but these plans were never realised.
It should be noted that Post Great Schism, Atriox and his followers are aware of the existence of other Covenant splinter factions. The Banished do not associate with them, however, and actively look down upon most of them with disdain/contempt, especially those that continue to honour the Great Journey and the Forerunners. Whilst not necessarily true for each and every one of his followers, Atriox himself is an atheist, viewing faith as outdated and unnecessary, and unlike most of the other splinter factions, The Banished are thoroughly irreligious. As such, they raid and plunder systems across the galaxy simply to support their own goals.
Conflict with the Spirit of Fire
Atriox would eventually lead his forces to take over the Ark a month after its portal had closed, massacring the humans present on the structure. How Atriox came to know about the existence or location of the installation is unknown, but Atriox brought the entire Banished fleet with him. His goal was to create a Halo Ring and unleash it upon the galaxy. Before these plans could be realised, however, the crew of the UNSC Spirit of Fire landed on the Installation four months later, bringing them into conflict with Atriox and the Banished.
By this point, Atriox's forces were well entrenched and they allowed the humans to land without resistance. When Spartan Red Team entered the research facility they found the A.I. Isabel, as the sole 'survivor' and came face to face with Atriox. Despite the Spartans best efforts, Atriox made short work of the highly trained warriors, wounding Duncan in the process. Forcing the super-soldiers to retreat, Atriox mocked them as 'Little Demons' before ordering his bodyguards to finish them off. By this point, the research facility was surrounded by Banished, and the Spartans barely escaped with their lives.
This success was short-lived, however. Although Atriox had hijacked the Ark's portal network, allowing him to teleport his troops to anywhere on the Ark, Captain Cutter and his humans proved to be just as strategically gifted as he was. Striking at key positions across the Ark's surface, they managed to put up fierce resistance and became a serious thorn in Atriox's side. Delaying his plans and weakening his forces, they eventually managed to kill Decimus and destroy Atriox's flag-ship, which angered the Brute no end.
It was at this point that a Halo Ring emerged from deep within the Ark. Despite his previous setbacks, Atriox was quick to seize the initiative, ordering Let' Volir to get as many of the Banished as possible onto the ring in order to claim it before the human forces could. At this point, Atriox contacted Captain James Cutter, acknowledging the Captains skill and offering to let him go peacefully if he abandoned both the Ring and the Ark. Recognising the danger Atriox posed to the galaxy, however, Cutter refused him.
Atriox's efforts came to nothing, however, as the humans not only shut down the teleportation systems but Professor Anders managed to separate the land that the Banished was stationed on from the ring, eliminating all of them. As the Professor steered the ring through a portal, thus taking it safely beyond Atriox's reach, the Jiralhanae warlord vented his fury on the holo-table, enraged at the loss of his prize. Despite the loss of his prize, Atriox survived along with a legion of his forces and began preparing for his next skirmish with the UNSC.