Both the Ancients and the Ori evolved from a race known as the Alterans. Millennia ago, in a distant galaxy, the Alterans were a human society on an evolutionary path to ascension. However, a philosophical division grew, and those who became more and more fervent in their religious beliefs tried to wipe out the others of their race. Those who recognized the potential abusive corruption of these religious beliefs favored science instead and believed absolutely in free will. Rather than go to war, these Alterans built a ship, left their galaxy behind, and came to the Milky Way where they eventually ascended and came to be known as the Ancients. Those they left behind were known as the Ori. They too learned to ascend, and they passed down a religion called Origin to the next evolution of humans they created.
As ascended beings, the Ori have evolved physically and mentally to the point that they have found a way to shed their physical bodies and live as energy on another, higher plane of existence with an enlightened understanding of the universe and all its knowledge. In the physical world, the Ori manifest themselves as fire, flames of energy capable of entering and speaking through a human being. Fire has become the central icon of their religion, a symbol of light, energy, and warmth which has become associated with demonic imagery on Earth, perhaps due to the influence of the Ancients who would contrast good with evil, heaven with hell.
The Ori draw their power from the worship of the humans who devote themselves to the religion of Origin. There is a real, physical transfer of energy to the Ori that occurs simply through a human being's belief in them, however, for it to have a measurable effect, it requires massive numbers of humans relinquishing their will. Origin promises its followers knowledge, enlightenment, and the reward of eventual ascension, however the central promise of the religion, and everything Origin's followers devote themselves to, is a lie. The Ori conceal the truth of their existence from the people, and they do not offer their followers ascension as they promise, for in doing so they would have to share the power they draw from those who worship them. By sapping the life force of those willing to surrender themselves unquestioningly to them, the Ori offer a promise of salvation that leads to nothing but death of the most meaningless kind because there is no conscious effort to achieve enlightenment without being blindly led by the Ori.
Although the cultures of the Ancients and the Ori have similar roots in a shared language and very similar technologies, it is the doctrine of noninterference that most clearly distinguishes the Ori from the Ancients. The Ancients believe so strongly in free will that they will not use their knowledge to intervene in the affairs of the lower planes even if it means the destruction of an entire galaxy. In fact, the Ancients have been shielding the existence of the Milky Way Galaxy from the Ori to prevent interference from the higher planes. In contrast, the Ori believe that because they are ascended, all humans should worship them, and those who don't are not worthy of life and must be destroyed.
The teachings of Origin are expressed in the Book of Origin, the holy text that weaves doctrines into simple, fable-like narratives designed to teach meditation on one's worth and significance, the path of righteousness toward a state of higher being. Followers are taught that the holy book offers the path that will lead believers to enlightenment and ascension. Devotion is rewarded, those who stray must be guided back to the path, and those who reject the path must be destroyed, for it is the will of the Ori that Origin must be spread to all those blessed by their creation.
To spread the teachings of Origin, the Ori rely on a special class of missionaries called Priors. Priors are human, but through the Ori they have been granted special powers and access to the secrets of the universe. They are not complicit, however, for they believe the lie that they will achieve ascension. They are instead merely pawns in the Ori's grand scheme, and the more worlds the Priors convert, the more powerful the Ori become. The leader among the Priors is the Doci, the one who speaks the word of the Ori. In the holy city of Celestis, the seat of the Ori power where monks prepare to become Priors, the Ori manifest themselves as a wall of fire known as the Flames of Enlightenment. As these flames enter the body of the Doci, the Ori speak through him. To Daniel, the voice of the Ori declared, "We do not require blind faith, only that you believe what you see and know to be true. We are the Ori. We are their creators. All who follow the path will join us in enlightenment. Those who abandoned the path are evil. They have shielded you. The truth of the universe has been obstructed. All will know the power of the Ori."
When the Ancient communication terminal allowed Daniel and Vala to communicate in the Ori galaxy through the bodies of Harrid and Sallis, the Ori became aware for the first time of the existence of the Milky Way Galaxy, and the Doci vowed, "Evil has raised a great many unbelievers in a far-off place. They must be shown the path. Great holy armies shall be gathered and trained to fight all those who embrace evil. In the name of the gods, ships shall be built to carry our warriors out amongst the stars, and we will spread Origin to all the unbelievers. The power of the Ori will be felt far and wide and the wicked shall be vanquished."
As ascended beings, the Ori aren't able to take action in this galaxy without inciting the Ancients, however the Ancients would not prevent an invasion by the human followers of Origin. The holy crusade began with the arrival of Priors in the Milky Way Galaxy. With technology sufficient to establish a wormhole between galaxies, the Priors arrived by stargate on worlds such as P3X-421 where they spread the teachings of Origin and performed miracles to prove their claims. Their goal was not to destroy the populations but rather to conquer and convert, but those who refused to embrace Origin were shown no mercy. On P8X-412, a plague decimated the population until they succumbed. The plague would reemerge on numerous worlds, including Earth, and devastation such as the R75 species of insect was also traced to the Priors. One world after another fell to the power of the Priors, including allies such as the Sodan, Tegalus, Hebridan, Langara, and numerous Jaffa worlds.
On Kallana, the Priors prepared for the arrival of the armies that would follow them by establishing a beachhead that would collapse the planet into a singularity and allow the formation of a supergate and a permanent wormhole from the Ori galaxy. Although the supergate at Kallana was destroyed by SG-1, another supergate was eventually discovered near P3Y-229. In the Ori galaxy, human warriors by the tens of thousands, raised since birth to follow the Ori without question and to kill all unbelievers, built vast ships and prepared for a full-scale invasion of the galaxy. The impending "Doomsday," approached, the "Day of Reckoning when all who have renounced the Ori will feel their wrath." Their objective was conquest, for as more and more followers relinquish their will, the Ori power will increase until they are powerful enough to achieve their ultimate goal. The Ori are coming to kill the Ancients.
The Odyssey, the Korolev, and an armada of ships of the Jaffa, Tok'ra, Asgard, and the Lucian Alliance faced the four Ori warships that entered the Milky Way Galaxy through the supergate, but they were no match for the immense power of the Ori ships. The galaxy's greatest threat, however, was an infant, born during the battle. During the time that Vala had spent in the Ori galaxy, she had discovered that she was carrying a child that was "the will of the Ori." Her child, the Orici, held the knowledge of the Ori in the flesh and blood of a human, and provided a means for the Ori to enter the galaxy without confronting the wrath of the Ancients. The genetically altered infant grew within days into a young woman who took the name Adria and commanded the Ori armies.
SG-1's daring plan to activate a wormhole between the supergate and the Pegasus Galaxy succeeded in preventing additional Ori ships from entering the galaxy, however many more worlds fell to the invaders, including Chulak and Dakara. Their only hope of defeating the Ori lay in the Sangreal, Merlin's weapon capable of destroying ascended beings. Fearing the threat of the Ori, Merlin had retaken human form to create the device and had hidden it from the Others. SG-1's quest for the weapon had led them eventually to Merlin himself, who had been preserved in stasis and who allowed his consciousness to enter Daniel Jackson in order that the weapon could be completed. Daniel and the device were captured by Adria, who transformed Daniel into a Prior, but in an elaborate scheme, SG-1 completed the device, activated it, and sent it through the supergate to the Ori galaxy. With no way to know if the weapon had destroyed the ascended Ori, SG-1 continued to face the human armies of Ori warriors. Their attempt to capture Adria was thwarted when Ba'al took Adria as a host. In her weakened state, Adria ascended, leaving in doubt not only her fate, but the fate of the Ori themselves.
Cross Reference: Adria, Alterans, Ancients, Ancient Communication Terminal, Anti-Ori Underground, Ara, Ascension, Ba'al, Book of Origin, Celestis, Chulak, Dakara, Day of Reckoning, Doci, Doomsday, Flames of Enlightenment, Hebridans, Kallana, Langara, Lucian Alliance, Merlin, Merlin's Weapon, Nerus, Ori Satellite Weapon, Ori Warriors, Ori Warship, Orici, Origin, P3X-421, P8X-412, P9C-882, Prior, Prior Plague, Prior Staff, R75, Sangreal, Sodan, Supergate, Tegalus, Ver Ager, Ver Isca
Episode Reference: Avalon, Origin, The Powers That Be, Beachhead, Babylon, The Fourth Horseman, Arthur's Mantle, Crusade, Camelot, Flesh and Blood, The Pegasus Project, Counterstrike, The Quest, Line in the Sand, The Road Not Taken, The Shroud, Dominion, Unending