The Ancients evolved from a race of humans that lived millennia ago but who faced extinction from a plague that was sweeping across the galaxy. Many discovered a means of ascending to a higher ethereal plane of existence, taking the form of energy. Other individuals, including humans, who have learned the path to true enlightenment, have also achieved ascension, and these ascended beings came to be known also as the Others.
In their ascended state the Others can remain invisible, or they can take a non-corporeal human appearance. They can retake mortal human form, however it is impossible to ascend again without the help of the Others. The Others possess extraordinary abilities including a kind of telepathic communication or exchange of spirit that shares one's innermost essence, as well as great powers to control the forces of nature or to cause tremendous destruction if provoked. However, despite these powers, the Others are guided by strict rules. Communicating with those not ascended is a violation, and taking action that changes human existence is forbidden and cause for banishment. Orlin was one of the Others who was banished for offering the people of Velona the means to build a weapon of defense.
The most sacred rule of the Others forbids the acceleration of the natural ascension process of those beneath. No lone ascended being may help a "lower," or human, to ascend, but if there is an exception, for any reason, a majority vote by the Collective can grant permission. Oma Desala operated beyond the rules of the Collective and was outcast for helping others to ascend. The infant Harsesis was placed in her care, and she taught young Shifu the path of enlightenment to achieve ascension. She ascended all of the Abydonians who were killed when Anubis destroyed the pyramid on Abydos. As Daniel was dying of radiation poisoning, she helped to guide him to ascension as well, but he, too, was outcast when he attempted to confront Anubis in the battle for Abydos. Oma Desala drew him away and returned him to human form with no memory of his time as an ascended being, but she offered him a second chance to ascend after he was killed by the Replicators. Oma had been permitted to continue to guide others to ascension, always under the watchful eyes of the Others, because it was she who had unwittingly helped Anubis to ascend. Although the Others used their collective powers to keep Anubis from affecting anything on a grand cosmic level, Oma Desala's punishment was to watch the consequences of her actions, powerless to intervene.
Cross Reference: Abydonians, Ancients, Anubis, Ascension, Harsesis, Daniel Jackson, Jim, Kheb, Monk, Oma Desala, Orlin, Shifu, Velona
Episode Reference: Maternal Instinct, Absolute Power, Ascension, Meridian, Abyss, Full Circle, Threads