The Ori backstory is elaborate and is explained over Season 9 and 10 and the film Stargate: The Ark of Truth. Robert C. Cooper considered the backstory "pretty complicated" but felt the show gives the answers to the audience members who wanted to delve deeper.
Part of this backstory goes back to the Ancients, whose backstory began in the Season 1 episode "The Torment of Tantalus". Early in Season 9, Brad Wright explained that the Ori are the original Ancients, who would disagree with the Alterans (later to relocate and be known as the Ancients of the Milky Way galaxy) that they shouldn't interfere because interference would mean playing god, which these beings hadn't quite achieved.The Ori behave like gods in their galaxy, and are accepted as such on the grounds that they empower humans to seemingly perform miracles as proof of their divinity.Despite the fact that their method of ruling is oppressive and even cruel to those who defy them, they see themselves as benevolent, because they offer all the knowledge of the universe and way to ascend. "There's a twist, and we're not going to reveal that part. But there's a real sinister, evil quality to what they're doing, and why.
As told in the series, the Ori and the Alterans (later known as the Ancients)formed one race millions of years ago and lived in one society on an evolutionary path to ascension. However, a philosophical division emerged. The Ori grew more and more fervent in their religious belief, while the Alterans adopted a more scientific/rational outlook to become a more progressive society. According to the Ancient Myrddin, the Ori had the best intentions when they first began. With the Ori outnumbering the Alterans, their viewpoints ultimately diverged so much that the two groups split apart and began to oppose each other, with the Ori attempting to kill the Alterans.The Ark of Truth flashbacks to human Ancients coexisting with the people who eventually became the Ori. Their ultimately different beliefs in regards to science led to the Ori to threaten to kill the Ancient scientists, and out of self preservation, the scientists chose to hide their level of scientific belief so that they would not get into a conflict. Eventually, the Ancients decided to build a space ship and leave rather than to use their technology like the Ark of Truth to defeat the Ori,, mainly because they thought it to be philosophically and morally wrong.The film thus addresses the non-interference policy of the Ancients under the Ori threat, and how they act since SG-1 did them a big favor by killing the Ori.
After much time, believed by Daniel Jackson to be thousands of years, the Alterans discovered the Milky Way, where they eventually built their empire. However, even after the Ori had forced the Alterans to leave their galaxy, the two factions remained bitter enemies. Eventually, the Alterans were afflicted with a terrible plague that wiped out most of their civilization.It would later be discovered that what was known of this plague is very similar to the disease used by Ori Priors against non-believers, which had led Daniel Jackson to speculate that the pre-Ascended Ori might have been responsible for this plague.
After millions of years, both the Alterans and the Ori learned how to ascend and evolved, forming two groups that continued to oppose each other, even at the higher planes of existence. According to the Orici Adria, the Ori-Ancient war on the Ascended plane is due to the Ancients' intolerance for those who do not comply with their rules.According to Orlin, the Ori ultimately wish to destroy the Ancients once and for all.The Ori had thus become ascended gods without physical bodies in the human plane of existence. Still, they are a localized energy form that is not entirely omnipresent in the universe.
The Ancients are well known for their fierce belief in free will[episode needed}and have a code to be "fairly non-violent". As such, they do not interfere on lower planes of existence at all, not even to save their own kind from being exterminated by the Ori.In contrast, the Ori constantly interfere. For example, their religion states that failure to share the secrets of the universe to those on the lower planes of existence is an evil act and that anyone not following it must be eliminated. They also have no rules against taking direct control of living beings or completely changing them to behave as they desire.
According to a de-ascended Ancient, Orlin, ascended beings can be empowered by massive numbers of humans worshipping them. The Ori have fabricated an entire religion based on the false promise of ascension to drain power from their followers. The Ancients firmly resent using their powers this way, and therefore refrain from interfering in the lower planes of existence because manipulating and aligning lower life forms in some order could result in exactly this type of abusive corruption.
While the original ascended became the Ori and re-created humanity (the second generation of humans) to worship them in the Ori galaxy, and gave their followers the technology to essentially enslave others to enforce them to believe as the Ori wanted them to,the Ancients have shielded the second evolution of humans (i.e. current human culture) in the Milky Way from the Ori and still prevent the Ori from taking direct action in the Milky Way. However, as the Ancients will not interfere in the lower planes of existence, the Ori are allowed to send their human followers to the Milky Way in order to convert it, and anyone who wishes to worship the Ori will be allowed to do so.
